You're not willing to explain your reasoning behind this, though?

I think he's trying to explain it, but he speaks so consistently within the jargon of the game book that when there are differences of understanding it becomes difficult to pick out exactly what he means, sometimes.

As for the example of "getting shot", I suppose I should have expected such an obvious response. But it doesn't address my question at all - I was using "getting shot" as an example of a "hard move", separate from the action being described. I was hoping people would understand the thinking behind my question instead of playing "gotcha" with my particular example.

I'm not sure whether that's aimed at me or at Vincent.  If me, I should point out that I did not mean it as a "gotcha", but as a genuine explanation of how it's meant to be played.  In just a moment, I'm going to explain what might happen if you don't get shot, using your own example, as I understand (and use) the rules.

For instance, let's say I'm trying to escape from my captors. I use a sharp stone to slit my bonds, and I run out into the courtyard. I bump into a guard; he's got a pistol in a holster, and he's standing in front of the door (the exit). He hardly has time to react, except to bring his arms up to hold me back. I charge at him, head down and fists swinging. We decide this is me Seizing by Force - I want to get to the door, to "fight my way free".

When is it legit for you, as MC, to say that I'm not quick enough, and that the guard manages to draw his weapon and shoot me?

Let's make three sub-examples out of your example here.  In both of them, you're unarmored (because of course they removed your armor when they captured you) and you're a gunlugger with the Not To Be Fucked With move, and you're using the "fight your way free" variant of the Seize By Force move.

• You roll 7-9: You suffer little harm.  You take definite and undeniable control of it (or, in this case, you definitely and undeniably fight your way free).  You charge the guard and get to him before he has time to draw his gun, a .38 revolver (harm 2), so you manage to shove him aside so he lands on his back, incidentally taking an elbow to the ribs on your way out, suffering one harm that gets absorbed by the fact you count as a small gang versus a single individual (+1 armor).  Rather than stick around and pick up his gun or beat him to death, you rush out the door and escape around the corner of the building before he can gather himself enough to exit the building and shoot you in the back, and before reinforcements arrive.
• You roll a miss: You suffer little harm, and that's the only outcome option you can have.  You charge the guard and get to him before he has time to draw his gun, a .38 revolver (harm 2), so you manage to shove him aside so staggers away from the door, incidentally taking an elbow to the ribs on your way out, suffering one harm that gets absorbed by the fact you count as a small gang versus a single individual (+1 armor).  Because you do not take definite and undeniable control of it (or, in this case, definitely and undeniably fight your way free), he doesn't take as long to get himself together and gets to take a shot at you before you get around the building.  You now need to Act Under Fire to get away.  Maybe a 7-9 "flinch, hesitate, or stall" means you take a shot in the back, but still get away for the moment; maybe a miss means more of the gang shows up.  Alternatively, maybe a 7-9 means you get around the corner, but he saw which way you went; then, maybe a miss (prepare for the worst) means he shoots you in the back.  The MC should play these consequences as things fit the "fiction".
• You roll a miss: You take definite and undeniable control of it (or, in this case, you definitely and undeniably fight your way free).  The guard gets his .38 clear of the holster just as you slam into him, and reflexively pulls the trigger, shooting you in the leg, then he falls on his back and his gun flies across the room.  Two harm, minus one for Not To Be Fucked With, applies.  You still manage to rush through the door and around the corner before he can see where you go or reinforcements arrive.

On a hit, you might get shot anyway, but the default assumption seems to be that you'd have a chance to react, first. (For instance, maybe you get past the guard and are rushing out of the place when he draws and fires - and here you'd get a chance to try to avoid that, if circumstances allowed that.)

The way it works now, I'd say, is that your roll determines how many advantages you get to choose, and whether you get to the guard before he can get his hand on his gun is one of those potential advantages.  Another is how far you manage to get when you fight your way free before the MC throws another move at you.  Another is whether you kill the guy when his head hits the concrete floor so he can't call for help.  Another is whether you impress, dismay, or frighten him so he just doesn't come after you at all once you're past him.  The consequences are the player's to choose; the MC just describes them, really.

NOTE: Cross-posted with Ebok, above. I think we're in agreement. It seems like the intent here is to make "Seizing by Force" not an uncertain, risky action, but something you weigh against the cost (in harm/damage/casualties) instead. Is that the design goal here?

Keep in mind that every time harm is done you have to roll your harm move.  What happens to your escape if you lose your footing when you get elbowed in the ribs, even if the harm total is zero?  What if you miss something important, and the MC thinks up some consequence that will surprise you as a result (like another guard outside, an alarm of some kind that you trip on the way out, a lookout or sniper on a neighboring building, or someone following you discreetly to find out where your friends are hiding with the loot you stole from the gang who captured you for the sake of interrogating you for that information)?  Every time there's an exchange of harm, right there in the description of the move you choose to use, consider that something might go awry when you roll your harm move as well.

I forgot to mention something kinda important in my last long post, and I had something in mind to mention in this long post that I've forgotten as well.  I don't recall either at the moment, so maybe I'll remember to share both at some later time.

Note 1: I've provided a TL;DR summary at the end.

Note 2: Please be gentle.  This is my first post on this forum.

My take on all this is that there are some fundamental principles that apply to how one should interpret, and use, Seize By Force.  These principles imply an approach to adjudicating these matters as MC, but the implications may not be obvious to everyone, so I'll lay them out here.

The salient principles, as I see them, are:

• Be a fan of the PCs.  They're cool.
• The names of moves describe what happens.  If you "seize by force", you "seize by force" -- you don't "try to seize by force".  If you "do something under fire", you "do something under fire" -- you don't "achieve the thing you want to achieve".
• The work your character has to do, and the complications of the conditions, inform how you go about giving your PCs a path to success.
• Players, like MCs, should make decisions to serve the story.  In the particular case of players, "serve the story" is mostly focused on serving dramatic character development, where for MCs it's about serving dramatic plot development, because RPGs in general are (ideally) character-driven from the players' points of view and plot-driven from a GM's point of view.
• The chances of failure in combat in Apocalypse World's die roll rules are higher than is typical for other games, because of the fact fewer rolls result in bigger consequences with less opportunity to amortize the pain of failed rolls over time, softened by successful rolls.  When one roll often concludes combat, "you're screwed" as the consequence of every move in the game with an average (or more than average) chance of a "miss" can be catastrophic -- not just now, but a shockingly large percentage of the time, to the extent that it can even be catastrophic for players' enjoyment of the game.

The result, then, is this:

If you what the PC is trying to do is straightforward and direct, and the PC is acting from a position of strength, just use Seize By Force.  Do not assume a "prepare for the worst" consequence of a "miss".  There may be a direct cost involved if the player doesn't really nail the roll, depending on the stats; low armor versus well-armed opponents with a miss on the roll for Seize By Force means a choice between taking harm and achieving the stated goal.  When the stats say no harm, and the PC (mostly) only really cares about success at the stated goal, though, this is a moment for the PCs to shine, to be cool, to accumulate accolades from players and MCs alike, who should all be fans of the PC (see point 1 above).

I think it's time for concrete examples.  Let's say you're trying to protect someone:

If you're taking direct, straightforward action from a position of strength, of course you use the Defend Someone Else From Attack variant of the Seize By Force move, and you're effectively guaranteed to succeed at that narrow goal.

If what the PC is trying to do is attempted from a position of weakness, indirect, or otherwise complicated, another move might be more appropriate.

• If you're in a chaotic battle situation where you don't have a commanding, central presence, with a gang running rampant around you, and you aren't even close to the person you're defending, you might be forced to provide indirect protection in the form of tactical and support moves like the Stand Overwatch move, where it becomes very difficult to effectively intercede on your ally's behalf apart from giving warnings.
• If the approach the PC takes to defending someone requires some (relatively) complicated series of actions that detract from the overall potential for success, is for the MC to just tell you "No, you don't get to Seize By Force (yet).  First you have to get there.  How are you going to do this?  If you're trying to get to the guy to physically protect him while raining autofire on the enemy, you're first going to have to Act Under Fire to cover the intervening ground."  Perhaps the MC has a countdown/clock for the consequences of you failing to get there "yet" every time you fail.  Maybe it takes one 10+ result ("you do it") with one tick of the countdown clock to get to a point where you can then use Seize By Force to determine exactly how you save the day in a grand, heroic manner; maybe it takes two 7-9 results ("you flinch, hesitate, or stall") with one tick of the countdown clock (and its attendant consequences) for the each of those two Act Under Fire rolls; maybe every time you miss on Act Under Fire you get nowhere and another tick of the countdown clock brings further consequences.

Once you maneuver to a point where Seize By Force is the only reasonable move, in either of those examples of acting from a position of weakness, the purpose of the move is more to determine how you achieve your goals, and with how much of a dominating presence, rather than whether you do so -- unless you think your character might actually opt for taking no (or less) damage during the exchange of harm rather than effectively defending someone on a "miss", if that's possible given the relevant stats (or unless there's some other trade-off to be made, such as wanting to kill more enemies as a higher priority than wanting to actually defend someone).

Remember, too, that the conclusion of that move is not necessarily the end of the matter.  Now your character has defended the person from attack.  What happens next?  Maybe the PC has closed the distance and provided effective defense, but the PC and the defended person are now trapped, and under siege.  On a "miss" result for Seize By Force, you might choose to definitively seize control, but that means you give up on inflicting terrible harm; when fighting against a small gang, that means you've probably killed fewer gang members, seriously injured fewer, and lightly injured fewer, which reduces the likelihood the enemy doesn't count as a small gang any longer (thus changing relative armor and harm values).  You've also given up on impressing, dismaying, or frightening your enemy, thus reducing the likelihood they'll turn tail and run in the face of overwhelming force.  The negotiation between MC and players to define the ongoing flow of dramatic action should change based on the results of that roll, as the degree of success informs the discussion.

In summary:

Seize By Force is the straightforward "PCs do awesome things" move that applies when action is direct, and undertaken from a position of relative strength.  If some other behavior is required to get to the point where Seize By Force is appropriate, the chance of success or failure is the accumulation of several rolls, with Seize By Force just being your "finisher" move at the end.  Once again speaking of the example case of defending someone else, if something less certain is more appropriate because of a need for indirect action (e.g. tactical support moves) or not being able to assert a good offense as the best defense so that you only get to try to save someone at the last minute from a sniper's headshot with a tackle (e.g. Act Under Fire), do that instead of Seize By Force.

As a result, there's nothing at all wrong with Seize By Force not having a failure contingency built into it.  It's not for circumstances where that kind of "failure" applies.  It's just a move that must be applied appropriately within a wider context.