I agree that character traits can have flipsides and conect to each other.
A virtue can lead to a flaw, and a weakness can lead to a strenght.
A couple of examples:
A kind person may struggle with taking care of themselves because they focus too much on the wellbeing of others
A physically weak character may rely on their intelligence and/or talking skills to get out of trouble.
Of course, the connections between these traits may vary from character to character. Someone may be strong and smart too.
It`s also important to take into account how they handle things outside their comfort zones.
While a person can`t be confident and insecure at the same time by definition, they can feel confident in the things they are good at, and feel insecure when doing things they struggle with.
For example: a magical girl does an amazing work defeating monsters, she may feel awesome and display a huge confidence when saving the day, But struggles with school. She may even get nervous during tests or social situations.
Also, their upbringing can affect their behavior. And some experiences can lead a character to change, or to try to change.