Do You Know What to Do in Different Situations?

Tennis, fencing and speaking are all about being in flow. You can't just focus on winning if you don't know how to do it. Think of it like flying a plane - everything's cool until the engine fails. Without any train, to just flip that switch is almost impossible. So i feel like you have to practice getting reps in,. losing your train of thought and pausing. It's where does confidence come from? What is confidence? Confidence comes from something you did in your past, right?