Why do we procrastinate?

So I'm sitting in bed right now, knowing damn well I have plenty of schoolwork I could be getting done, but am choosing not to do so. This led me to asking the usual question:

"Why the f--- do I knowingly procrastinate?"

I blame the human mind, as with many of my problems with the human experience. I believe that we were meant to be more challenged than we are today. Even if you are homeless, you're alive. Shit, when humans were in hunter-gatherer societies, we didn't have time to f--- around with video games, t.v., and the black hole that is the internet. If you didn't get shit done, you were directly affecting the rest of your tribe. We didn't have time to be lazy. 

And yes, I hold procrastination and laziness in the same light. I am a self-admitted lazy jerk. However, I feel like I (and all humans) have the right to. Animals act on instinct; they're relatively unorganized (or maybe too damn organized). We have gained the ability to f--- around and not get our work done, while animals are still just trying to survive.  

The bottom line, and unfortunately probably just one of procrastinations sinister tools (a.k.a. rationalization), is that I only have this one life, why would I waste it being unhappy while doing schoolwork? 

I'd much rather have fun. I advise my fellow humans to do the same. Put off that thing you have to do. Instead, kick back and watch a movie, or whatever you do for fun. That thing will still be there tomorrow, and you will be a little bit happier right now.