The tanden is a Chinese concept that encompasses the spirit, the will to win, and the drive to win which is a more important asset than power or strength. Even fear or nervousness may be translated as spirit.
Fear can work if one knows how to use it to one's advantage.
It can pick one up and pump one up. Use it as the greatest ally. The will to win and the excitement of facing an opponent force a subconscious defense mechanism which pumps adrenalin and strength into one's body. One's mental attitude, which starts in the belly, is very important to accomplishing any objective. One by nature has the natural ability to succeed.