Fear can be a good thing...but progression or approximity to the target. There is also imagery and stress reaction control...like breathing. If you can control your breath, you can control your emotions and thoughts. But your statement indicates that ur psyching your self out..."I do injure myself"...which is just re-inforcing the failure belief...what is your goal? To injure yourself or to hit a box? Instead of fear being the wall to overcome....you accept that there is fear and you start there. It seems that you are fearing fear. Its a combination of arousal (fear), skills and confidence...and in that equation fear is the challenge not a roadblock.