Do you think a pro athlete gets good by trying to fail, ever?

You deliberately get yourself pinned/knocked out you mean?

Yes. And especially for real world survival, beaten upon. Not to the point of causing injury to your organs, that's foolish, but destroying the ego within you that causes tension in your body that leads to physical damage. At least, that is a Russian way to look at taking a punch. The point isn't to become tougher, the point is to remove fear by dealing with fear. You cannot remove fear by insisting on being successful. From a combat perspective the question about professional athletes is just flat out wrong. I know that professional sports training must be grueling, but I have to wonder if non-combat sports that proceed towards a simple defined goal like "getting a ball into a basket" just aren't comparable to combat. I imagine the struggle of coaching and sports psychology, the internal struggle, is very similar though. They probably have to "invest in loss" even if the sport itself says "you must win."

Ask yourself this. Is a robot confident? I'm sure one could be programed to walk up to women, say something dirty, and take a slap. But of course it isn't confident. It's just a mindless automation with no ego to destory. Real confidence involves risk. Don't become a robot.