I think this is one of the oldest lessons in the book: be yourself. We've all heard it since before we could read, and it's so popular that it can become background noise at times. But it's a universal truth that only develops in complexity with age and experience. There's two benefits to knowing yourself: knowing your strengths and where they take you, and knowing how to act in a situation. Coach Bruce very clearly attested to this first part by saying "You can't be great at anything unless you're already good at it". In other words, know your talents and extrapolate from there if you really want to achieve greatness. This is monumental in finding a career. I know that my strengths lie in information processing, writing, and communicating. Even if my passions are elsewhere, I know that I should build on my strengths so that I can produce my best work possible. Why get a fish to run? This brings me a lot of peace when considering careers; there's many careers out there that are enticing and glamorous, but I know that I would be a fish out of water there, and I can achieve greatness still by extrapolating on what I already have. The second facet of knowing yourself is authenticity and acting out your truth. Coach Bruce exemplified this by comparing different coaches and their strategies. They were all different relative to each other, but consistent within themselves. This is a golden way to live. If you are being authentic to yourself, you can be at peace with yourself.
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