A chapter outline can be a useful tool, but don’t feel as if it’s engraved in stone. When you start forcing your characters to do your bidding instead of what they want to do, the reader will sense this disparity. Giving your character free rein often brings great plot twists.
When you find that your character wants to do something different than you’d planned, this is an excellent sign that you’ve created a credible one. Cardboard characters are like puppets and will do exactly what you tell them to do, but they also won’t be convincing individuals. No real person is 100% predictable and your characters shouldn’t be, either. If he or she gets himself into more trouble, it contributes to your story, especially when you also allow him or her to find a way out.
I think it’s a lot of fun when a character is in a self-imposed bind that I have no clue how to solve. That’s when I just let him or her figure it out. If I don’t know how it’s going to turn out, it should add to the suspense, assuming the reader won’t know, either.