"What if I'm not strong or smart enough?"

You might not be, that's why you're trying to get better, the trick isn't being good at it to begin with, or you wouldn't need to do it at all.

"What if I do all the work and it doesn't matter?"

You aren't a magic being that isn't affected by things, if you are genuinely putting in the work, you will get results, it might not be as quick or perfect as you think, but that's fine, you can make adjustments, and one of those adjustments might just need to be to your expectations.

I'm talking to myself today, and y'all are getting caught on the ride.

@RickiTarr
Or my other answer to the devil is "At least I won't be spending eternity with Donald Trump."