Why?

Why do we constantly fight the things that we know are good for us? I know for a fact that working out and eating healthy is not only good for me, but I actually feel better when I take care of myself. So why do I always fight it? Granted I can always dish out a bunch of excuses as to why I didn't have a spare 20 minutes to take care of myself....but that's just retarded! I NEED to take that 20 minutes to take care of myself every day. Yes, there may be days where I genuinely can't get around to it, or I'm too exhausted to, but even on those days I should make an effort to eat healthy, and if nothing else do some wall pushups throughout the house once in a while.