on Writers Helping Writers:

We’ve talked a lot around here about why characters need flaws. Those negative traits make characters relatable to readers, they contribute to their arc, and, oh, a whole bunch of other things. Flaws are especially important for any character navigating a change arc, where their weaknesses are keeping them from success and growth is necessary for them to realize the need for change.

Most of the time, creating flawed characters isn’t too hard. But it’s more difficult for certain kinds of characters than others—particularly if you’re writing a character defined by kindness or niceness. This is the nice guy/girl trope, and while it can work for a protagonist, it’s most often reserved for secondary characters, such as a friend, ally, or love interest.

The nice guy or girl is defined as being a decent, kind, and morally upright character who tends to make good decisions. That makes the question of flaws more challenging because this person, by definition, is good. It’s their defining trait, what readers should associate with them. The key to making to make this kind of character realistically flawed while still maintaining their defining goodness is to be careful which negative traits you give them.