This.
Maybe I can relate to how you feel, but I can never fully understand it, in the exact same way that you can't understand how I feel. Not because we're all just misunderstood people, but because our perceptions and situations are just different. The fundamentals may be the same, but the results are not.

The competition ("I'm depressed, too". "I have it way worse than you") bit makes me devalue my own feelings to a serious extent, which isn't healthy. I get that, but I think I might just always feel that I don't deserve to feel the way I do, because I know a lot of people have it a lot worse than me.