Ask Xtian - Super Bowl Edition

Evil

Dear Xtian- With the Super Bowl less than 2 weeks away, I had a football-related question. What is the difference between the 4-3 defense and the 3-4 defense? More specifically, why do people always talk about it like it is fundamentally such a big deal for a team to play one defense vs. the other? Can't players be flexible enough to play both defenses, and switch up as the game conditions dictate?