If you're writing fiction, you may think the sky's the limit, that you can push and pull your characters through your story, acting out whatever outlandish scenario or surprise twist your imagination can conjure up. Not so. Readers have no patience with characters who act, well, out of character. If your brave, muscle-bound hero becomes suddenly weak-kneed at the idea of being trapped in an elevator, he'd better have a good reason (maybe he was locked in a dark closet by an evil babysitter as a toddler).
Characters, real or imaginary, can be motivated by external forces; war, natural disaster, the loss of a job or a loved one are a few obvious examples. But more interesting, and more difficult for the writer to portray, are the internal motivations-the fears, ambitions and desires-that drive people toward or away from events, situations and other people.
As we look at the process of building a character, remember that traits and motivations are closely linked. A character may have a personality trait-shyness for example-that results from a physical trait-a stutter, let's say. A personality trait can also result from an experience in a character's past-your shy character may have been publicly humiliated by a bully in school. But however you justify the shyness, it becomes a motivating force behind this character's actions in your story. And if your story calls for your character to overcome his shyness and speak publicly to an audience of thousands, he'll need strong motivation for that as well (maybe the speech is necessary to raise money for a cause of vital concern to the character)