I go to the gym each morning. I get on the treadmill, or the bike, or the elliptical, and I exercise for an hour. I can't help but see myself in the mirror, and I see a fat guy that is breathing heavy and sweating like crazy. I see a man in terrible shape, short and chubby and a big blob. And I think, "what on earth are these other people thinking when they see me?"
Here's the answer. They don't see me. Oh, sure, they see that I am a guy on a treadmill. Beyond that, though, I'm invisible. I could be anyone and it wouldn't matter. Why? Because they don't care about me. They are too busy thinking about their own bodies, their own routines, their own struggles and successes and to-do lists, etc, to spend any time bothering with me. They are not worrying about me or thinking that my legs are short or my belly is big or whatever crazy self-criticism I have at the moment.
So no one is criticizing me. No one is judging me. No one is expending energy to attack me. In fact, no one cares. And that's a good thing.