How much does your own confidence improve your performance?

I notice that it plays a huge part in my plays. In my head when the stakes are low I can do so much more it feels like. See an off angle or do mechanically better when I’m in the zone. But once I feel that I’m underperforming I’m starting to tunnel vision stop thinking and my mechanics are dropping significantly. How do you maintain the confidence especially when you see yourself falling behind your own teammates?