We simply don't react the way that we think we will. Writing stories is no substitute for real life, it is just a ghostly apparition of what might be. This statement often comes from a need for power and control, or untested belief in one's abilities or strength. Writing honestly is closer to real life because you shape the characters with the strengths and abilities you want them to have, and some people really will act as you have written. If you have tapped into the right situations and feelings, the result is an engaging story.
Honest writing is a worthwhile goal to reach for.