• Noun: the supreme effort one can make; example: "they did their best"
• Noun: the person who is most outstanding or excellent; someone who tops all others; example: "he could beat the best of them"
• Noun: Canadian physiologist (born in the United States) who assisted F. G. Banting in research leading to the discovery of insulin (1899-1978)
• Verb: get the better of; example: "the goal was to best the competition"
• Adj: (superlative of `good') having the most positive qualities; examples: "the best film of the year", "the best solution", "the best time for planting", "wore his best suit"
• Adj: (comparative and superlative of `well') wiser or more advantageous and hence advisable; examples: "it would be better to speak to him", "the White House thought it best not to respond"
• Adv: in a most excellent way or manner; example: "he played best after a couple of martinis"
• Adv: it would be sensible; example: "you'd best stay at home"
• Adv: from a position of superiority or authority; examples: "father knows best", "I know better."
I don't think you can ever do your best. Doing your best is a process of trying to do your best.
But to be the best, you must face the best. And to overcome your fear, you must deal with the best.