agree with above and word choices/descriptions play a part to. Ultimately, it’s through the actions and their reactions to their environment and people around them.
Example of MC being: “I can do this. I know I can.” MC pumps himself up, paying homage to Bruce Lee his idol and looks to his ribbons and shiny trophies for reassurance.
Example of MC being depressed: “Why don’t they appreciate me? Everyone hates me.” MC looks down to his feet feeling downcast. His room feels heavy, dull, empty and boring.
Example of MC being stoic. MC friends are hesitant to invite MC out to MickD’s for lunch. “He’s pretty quiet these days. Usually, he jumps to the invite but he coolly shooed me off. I don’t feel like I can talk to him anymore.” gossiped SC friend.
Excuse the bad writing. Hopefully, this helps a bit.