Prompt: I believe it is harder to be fair to oneself than others
The sentence is perfectly correct as it stands, if that's what you're worried about. Do you not understand the meaning? Is that the problem?
It means (the speaker believes) that people have a tendency to hold themselves to higher standards than they hold others to; they expect more from themselves than from others; they're less tolerant of their own mistakes than those of others; they treat themselves more harshly than they treat others. Something like that.
Heeeeeeelllllllppppppp us heeeeeeelllllllppppppp you.
But it's only true of kind people. For hypocrites and egoists, the opposite holds.