Remember your main character needs to have a fatal flaw. It doesn’t have to be evil; it could be something like being too honest or outspoken. No one is perfect and to be convincing, your characters shouldn’t be, either. It’s their weaknesses that make them more endearing and real. They also build suspense, an essential ingredient for any story.
If you’re not sure what a character’s fatal flaw might be, take a close look at his or her strengths. Any trait that can be a strength can also be a weakness, if taken to the extreme. Obsessions, for example, can go either way, to a person’s advantage or detriment, depending on the situation. For example, being determined and not giving up can also result in beating the proverbial dead horse.