"Incurvatus in se" is a fancy Latin phrase that means a person is very focused on themselves and their own problems. It's like they are in a little bubble and only think about themselves instead of thinking about others or the world around them.
Imagine you are playing with your favorite toy and you are so focused on it that you don't even notice your friend trying to play with you too. You are only thinking about yourself and your toy, and not about sharing or having fun with others. This is kind of like what "incurvatus in se" means.
So, if someone says that a person is "incurvatus in se", it means that they are very self-centered and they only think about themselves. It's important to try and think about others and the world around us too!