Many people have trouble thinking of themselves as “good enough” unless told by someone else.
They often overlook their good traits believing others are way better and there’s nothing good about them at all.
But everyone knows that’s not true. Everyone has something in them they should be proud of.
The good thing about compliments is that it reinforces the action.
If what they did is good or they have good qualities, compliment them. It’s free. And it feels good to express it.
But never compliment the bad stuff. Otherwise, you’re reinforcing what’s bad. No reason to do that.