Blocking or Attacking the Attack

When punching I noticed a lot of people covering up and then after their opponent's finshes what they are doing, they attack back. Using boxing as an example, the only time you should cover up is if you are in trouble. You don't need both hands to block a punch. If you block with one, you can simultaneously hit with the other. Better yet, when someone starts attacking you, attack his attack. It's like interupting someone's speech. Don't let finish what he's trying to say. Here's a clip of my defensive philosophy. This clip is a 1994 boxing match. http://www.youtube.com/watch?v=WevTwdPMWFE