That point on aggression is a tricky one. Confidence comes from being competent, and that comes from practice, experience, and working within your envelope of capability.
I had one experience during Judo tournaments. One where there was a significant friendly competition and the aggression turned on immediately. In a different tournament, I was off my game, showed up on the mat, and expected to feel out an unfamiliar opponent. They smoked me with a simple but aggressive move. I lost out because I couldn't switch that same aggression on.
Perhaps the best place to turn that aspect on is through intense competition, and while that drives skills, it also can force you to nurture that baser part of ourselves and form it into a tool.
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