No good story begins with "Everything was the way it had always been been." Good editors cut out that part. The real story begins with the moment in time at which things can never be the way they used to be: when an action cannot be undone, a word cannot be unspoken.
In cinema and novels this point of no return is often on a grand scale. The one true ring is found, and the whole world stands in the balance. Or Hitler has just crossed into Poland. These are fine for the big stage of a movie theater or your mind's eye, but in improv we are limited in our resources.
Years ago, I had given some young students advice that I think might not be helpful for adults (or anyone for that matter) which I regret giving. I told them that because in improv we don't have props or sets or wardrobe, that meant we basically had an unlimited budget: you could summon a tyrannosaurus rex, or you could wear a priceless diamond ring.
Ultimately I felt this advice was not helpful because it introduced more possibilities rather than limited them. We are already faced with so many possibilities in our life; to introduce more into the paradox of choice is a recipe for anxiety and dissatisfaction. My advice now: the only prop you have is your partner.
Limiting these resources limits the frame of our stories. The story isn't about destroying the one ring and saving Middle Earth. The story becomes about Frodo bitching at Sam for leaving Lembas bread crumbs everywhere, and why can't he just clean up after himself? Middle Earth still needs to be saved, but the broader story becomes more of a set than the story itself.
Most stories in improv reflect the very real stories we reveal in day-to-day life through social breaches (which are a form of obstacle). If Michelle didn't call you back even though you know she received your call, or if Tony puked in your car after you begrudgingly gave him a ride, there has been a breach of our expected social order. We expect that Michelle returns our call at some point (unless she's dead). We expect that Tony will, like most of our passengers, not vomit inside of the car (especially when the window was open).
What happens next is anybody's guess. That's why it makes for a good story. The way that people react to obstacles reveals their true character. I'll say that again because it's axiomatic: the way a player reacts to an obstacle reveals their character.
Our character is not revealed by the good times that we spent eating ice cream and growing fat on good pay and no stress. It's revealed when the shit hits the fan, and you either lose your cool, or you hold it together. When Tony pukes in your car you can either keep it together or lose it because these are the options that any person has in that situation.
The funniest scenes, in my opinion, require a significant deal of resistance, especially when it comes in the form of an unusual choice. Let me explain a few different levels of resistance for the puking in the car scene.
No Resistance: The driver player, wanting to Yes-And hardcore, is totally OK with Tony puking in the car, and says "That's great! I love when people puke in my car. No problem, I'll pick it up later."
Full Resistance: The driver Yes-Ands the offer of antagonism and gets very upset. "Jesus Tony! Again? You do this every Saturday, and I'm sick of it!"
Some Resistance: The driver Yes-Ands the fact that Tony has just puked in the car, and treating the situation like a nice, face-saving person, they are very polite. "Oh. Oh, gosh. That's OK, really, it happens."
The puking Tony player, then in turn has a few options for responding to each of these levels of resistance (and of Yes-Anding). Let's say that in either case he is going to heighten and repeat by puking in the car again. In both the No Resistance and the Full Resistance examples Tony puking elicits more of the same: either support for puking (which is unrealistic) or greater disruption and name calling (which is uninteresting).
In the Some Resistance model, by puking Tony himself creates Some Resistance, by resisting the project of the polite driver to smooth everything over by acknowledging but forgiving the breach, returning to the status quo. "Oh, goodness. You did it again. Really, that's... a lot of vomit."
By putting up just the right amount of resistance we remain in the act of a social breach, suspended. In the No Resistance and Full Resistance models we either don't recognize the breach or we have, to some degree, left the breach by condemning it. By remaining within the breach and puking again in the polite man's car, Tony is testing the character of the driver, who has been met with an obstacle (which was, in part, his own politeness). We can remain on this threshold through mutual resistance to the others' project, creating a tension that keeps the scene in suspension.