At the crown of Roelof Botha’s otherwise perfectly coiffed, light-brown head of hair, there’s a small patch that’s gone completely white. It’s the result of a serious concussion Botha incurred in his twenties while playing rugby, his sport of choice in his native South Africa and in business school at Stanford. That injury ended his playing days. But spend some time with Botha—who’s now the head of Sequoia Capital, one of the oldest, largest, and most successful firms in venture capital—and rugb...