You'll basically have to figure it out for yourself, but I'll tell you how I might've approached the problem if I were you. The problem isn't overthinking per se, it's where you direct your attention. You can't actually put a halt to the thought process. When you instruct your brain to ignore something, it will automatically conjure up an image of what you're not trying to think about. The more you try to push it away, the more it sticks.
If you're already confident about an established belief (i.e. "I can achieve anything within the realm of karate"), then just let it be. Shift your focus to something that actually requires logical analysis, like how you could improve your diet.
Think about meditation. When you meditate, you don't actively try to stop the flow of consicousness by telling yourself "don't think about THIS". It's impossible. Instead you direct your attention to something else, like a visual image or perhaps your breathing. And when you do that, everything else gets pushed to your subconscious. So don't try to stop overthinking, just be more selective about your attention.  |