Thou shalt be changed by the world
This is not about having a character who changes through time and experience (although that's certainly good too). This is about the more immediate issue of changing what you can and will do in order to respond to circumstance.
We'll take an extreme case: when you're being fired at by a hundred crossbowmen, and a bare moment away from reaching cover, that is not the time to stop and deliver a long-winded speech. Even if your character is compelled to give a speech, the way to handle it is to start one and then accept that he'll fall down pincushioned with bolts.
Basically, I want you to act in partnership with the rest of the game world, not just use it as a backdrop. Use your circumstances as a way of showing new sides of your character! If your decadent fop is being hunted, perhaps he needs to hide out in a seedy motel where the grunge and poverty drive him nearly batty. If your soft-spoken little flower is in being accosted by rudeness, maybe you need to show that when her temper finally snaps it does so with a vengeance.
In short, even when you're dealing with circumstances that you wouldn't have chosen, you can choose to make something dramatic of them. This is particularly important in conversations: The flow of conversation is like tennis, with volleys going back and forth, and each player constrained in what they can do next by what has come before. If you just say "Well, enough about politics, let's talk about ME", it's like forfeiting the volley to start a new one. Doing this once or twice is fine... every conversation has its little twists and turns. But if it happens all the time it's a problem.