Remember your main character needs to have a fatal flaw. This is what allows your reader to relate to them. It’s also what makes them seem real. Flaws don’t make a person weak, only human.
Often when we think of flaws, we think of some disposition to do evil or propensity to fall prey to some horrible temptation. While this can definitely work, it’s not always necessary. A fatal flaw’s primary function is to stand between your character and what he wants.
Any number of character traits can fill the bill. It could be something as simple as being too honest, outspoken, having too much pride, lack of confidence, too impulsive, hot temper, doesn’t know when to quit, guilt over past mistakes, too idealistic, stubborn, easily distracted, too emotional, perfectionist, indecisive, spiteful, knows everything, control freak, unrealistic, etc.
If you don’t know, you need to figure it out. What do they have to overcome to grow as a person so they can get what they want?