- They may fail to tell me truthfully about their backgrounds.
- They may give me the wrong reasons for what they are doing.
- They may work hard, often in devious ways, to keep me from putting obstacles in the way or making them suffer.
- They may abandon me at inopportune times.
When I was a plotter, this didn't concern me too much. I already had lists of things that were going to happen to them, I had profiles that included aspects of their childhoods and their strengths and weaknesses, and I didn't depend upon their input. Since I approached the work with confidence and a clear idea of what I would write next, the writing went forward. And, eventually, the character got back to work.
I can still go back to my old ways and mechanically develop plots and profiles when pantsing fails, but I prefer to takes steps that are more in the spirit of improvising. When I do that, there is little violence done to creativity, and I get the surprises I'm looking for. Here are some methods I use.
Interviews. I have an advantage here in that I have played journalist through most of my career. I know enough to 1) ask open questions that can't be answered with a yes or a no, and 2) to listen to the answers. Most characters are easy interviews. They already know me and are willing to talk. But sometimes I need to get them drunk first. I literally imagine bringing them to a bar, sitting through several beers with them and then springing my questions. This may take more time, but it is worth it. Note: I do not actually drink myself during these sessions.
Traps. Sometimes I purposely put my character into a stressful situation. I write down the scene in vivid detail, including all the senses, and then shove the character into it. Once they enter the nightmare, they squirm and beg and reveal themselves. The trick here is making sure it is extreme and difficult for them. Many of my characters can laugh off situations that would tear me apart. I have to find their Achille's heels.
Changing Point of View. If the character (usually the protagonist) doesn't want to talk, maybe someone else does. I recently broke through on a story by having the villain narrate the scene. He saw himself as the hero and was eager to tell his side of the story. Once I had the whole scene down from his point of view, it was easy to write it from the protagonist's perspective. (Sometimes, this exercise has had a surprising result: it has shown me that I need an additional POV throughout the story.)
At times, I also find that I need to go back an earlier scene and rework it. I hate doing that. It stops forward momentum and it risks the kind of looping that can become pathological and unproductive. When I do go back to a previous scene, I limit myself to taking a closer look at the conflict. (This is something I always need to do in rewrites anyway.) Often, I find that I have dodged something that is painful to the character (and, likely, to me). Fixing that usually gets things moving again.