How can I fail or make a mistake and not feel like it's reaffirming what I feel I already know: that I suck?

Please realize that a set back is simply a set up for a come back. Instead of seeing something as a failure, see it as one more way to not do something. We all have times throughout each day where we feel we could have done better. We need to learn from those, and keep going. We are not finished when we are defeated we are only finished when we quit. Keep going, keep at it every day, it will be worth it. If you fall 100 times, simply get up 101 times and your winning.