Interesting anaology; one thing you missed is the role of a coach. A boxer is able to progress and improve his skills with the help of a coach. The coach helps identifies the boxer's main strengths, and the areas where he needs more training to improve performance. On the business world, entrepreneurs rarely have the willingness/ability to pay for a coach.
A boxer needs to develop strength, speed and stamina to be successful. What about a business person? I believe the key capabilities required are commercial acumen; a solid understanding of financial management and financial accounting; negotiation skills; and leadership skills. But above all, the ability to be resilient.
What about you? What do you think are the key skills required to be a successful entrepreneur?