This is a slightly unusual mailbag post because the question was asked in chat context, but it turned out to be something where I felt a number of other people would be interested in the answer, so I’ve paraphrased and expanded what I said there.
I have a story point where the protagonist has to do something. It feels bad not to offer them any choice here, but if they don’t do the thing, then the whole plot comes apart.
I have a bunch of tactics to offer here, depending on where in the story this is happening and what it means.
Tricks for the start of a story
Start the story after the choice has been made. “The protagonist has to do this thing” is a pretty common situation at the beginning of a game where we’re looking at the inciting incident for the story. You usually don’t want to allow the player to choose not to go on the quest for Smaug’s gold. It’s better to assume that, if the player’s started a game about this quest, they want to play the quest, and we should just get on with the first interesting choice that happens after they’ve already committed.
There are very occasional cases where I think an aesthetic argument can be made for including such a choice, but they’re very much the exception.
Tricks that work later
Shift responsibility for the incident. You can decide that some other, external force is responsible for the protagonist’s bad situation — which may then require some setup to prepare. This often works fine in an action/adventure-y scenario where we expect that misadventures will regularly occur to motivate the plot.
Alternatively, we can make the bad twist into an unforeseeable but inevitable result of an action that was perfectly sensible for the protagonist to do. Perhaps they’ve rescued a puppy, in line with their characterization as a lover of animals, only this particular puppy is the carrier of a disease that sickens all the other animals in the shelter. This is where the idea of the expectation gap becomes useful.
Provide strong motivation in the choice framing. The more one digs into this, the more the difference between interactive and non-interactive story starts to melt away. A non-interactive story can force its protagonist to do something stupid on command — but the viewer still wants to understand that this act is in character.
Maybe the protagonist did steal a car and take it for a joy ride and get arrested — but they did that because it’s a flashy sports car that their asshole brother bought and drove to Thanksgiving dinner just to show off how much better he’s doing, and it pushed all of the protagonist’s buttons at once.
The thing is that if you put that same level and quality of setup into an interactive story, and then you offer the player the choice
- Eat my turkey, keep my mouth shut
- Join Dad in congratulating Ryan on his brilliant career choices
- Pretend I need to pee, go outside, break into Ryan’s Porsche and drive it to Vegas
…there are pretty decent odds they will want to choose three.
And, if not, it’s also likely they’ll understand what the interface is communicating about the character if it’s greyed out the first two options as unavailable.
Skip the moment of decision. Use an act break or the space between episodes to skip ahead in the story until after the protagonist has done this.
This effect is distancing. The previous approach asks the player to think as much as possible in character with the protagonist, adopting their motivations and feelings so much that they do something that might not be in their own interests. This one, by contrast, pushes the player out of the protagonist’s head. Both can work, but they achieve different things.
You then do still need to reconcile the player to what’s just happened, though — justifying the protagonist at least in retrospect is often going to be critical to the player’s sense of themselves.
(I think my all-time least-favorite example of this is in Emily is Away, where control of the relationship is taken from the player in such a way that the protagonist engages in what could be construed as a dubiously consensual situation.)
One form of reconciliation is to make a mystery out of why the protagonist did this, and have the explanation gradually emerge through the next segment of play. I urge you not to motivate this via amnesia unless you absolutely have to, though.
Another approach is to show the aftermath of the Bad Choice, then tell what led to it in flashback. Think of all the TV shows that start with a shocking incident, then go back with “72 hours earlier…” to show how we got there. It’s a bit hackneyed, but it can work; and telling part of an interactive story in flashback mode means that we can ask some different types of question during this part of the story.
Which brings us to…
Useful any time
Offer a form of choice other than “what do you do?” Here are things you can ask the player instead:
How do you do this? Questions of method rather than intent are really common in Choice of Games works, and they feed into protagonism/identification forms of agency generally.
With what resources / at what cost / with what benefit? A bit related to “how,” but this choice gets the player engaged with the stakes of this part of the story.
Why do you do it? Motivation questions allow the player to put their own spin on an event. At the start of the game, this kind of question might let the player pick a backstory for their protagonist; later, it might have some other functions, like setting a new goal or calling back to a previous story outcome.
How do you feel about it afterward? A reflective choice with a slightly different flavor than the motivation question, often good to use as a character beat or a quiet moment between more action-y elements.
And then there are a few more esoteric options:
When, where, or with whom do you do this? All of your standard journalism questions are fair game for a choice point. And when/where/with whom questions can be good setup for an exploration or investigation sequence. Where do you go first? is a very common choice in a mystery scenario.
If there isn’t an obvious exploratory meaning, though, these questions may take a bit of framing to make them interesting — why does it matter where the player does the action? The answer to that might vary a lot depending on the narrative.
Sometimes from a narrative point of view it’s easier to think of these as resource/cost/benefit questions that just happen to be pegged to secondary characters or in-world locations.
You do this. What is the result? This one really flips the script, and sometimes it will feel deeply weird. But it can be a way to invite the player to co-authorship (at the more extreme/daring end of the spectrum). Alternatively, especially at the beginning of play, it can again let the player establish something about their protagonist’s family and home life. An example:
You put on a black leather corset with the red ribbon ties, and head for the front door. At which point…
- Mom completely flips out — something about the fate awaiting all immodest women — but I’ve heard it before.
- Mom completely flips out — wearing real leather is going to destroy the planet! — but I’ve heard it before.
- Mom doesn’t look up from her laptop long enough to notice.
The corsetry event always happens, with whatever inevitable consequence, but we’ve given the player the chance to pick one of three possible conflict engines with the protagonist’s mother: she’s a workaholic too busy to give us attention, she’s conservatively controlling, or her ecology-focused activism makes her hard to live with.
Emily Short's Interactive Storytelling 
There’s a very interesting moment of non-choice at the end of the game “The Last of Us.” The player character in that game has suffered some pretty traumatic experiences, and can be arrogant, selfish, and emotional. Throughout the game, though, the character’s hand is often forced by circumstance, and so it’s easy to fail to notice that his feelings about things may not align with the player’s feelings. That is, until the game’s climactic ending, when in a cut scene, the character makes a critical decision that is very likely not the decision the player would like.
It made me furious, but not in a “this is terrible design” kind of way – on the contrary, I’m sure the effect was exactly what the game designers intended. The player is allowed to forget that they are being asked to role-play a character who is not themselves, and then is brutally reminded of it in a shockingly unpleasant way that reflects the character’s own fear of lack of control in that moment.
In the end, explicitly taking the choice away from the player to represent a player character who is not in control of their emotions was a legitimate storytelling decision, and an effective one, in ways I would not have expected.