The great John Madden used to talk about this all the time, one of his many entertaining rants. In football certain numbers have a personality, a legacy, and by choosing that number a player sets a kind of course for himself.
After he puts it on for the first time, he has to live up to it. It becomes a crucial part of his identity as an athlete. Think of the great quarterbacks at Oregon who have worn number 10, or Dillon Gabriel choosing to wear Marcus Mariota's old number 8. The number has power. It foretells the way a player intends to carry himself.