I used to think when I was younger that if you knew what the right thing to do was, you would just do it. If you didn't do it, it meant you didn't really think it was the right thing to do. It's kind of like what Plato says, about how humans strive after the Good, and in a sense everything you do is good. Every decision you make is because you think it is the best decision.
But it's not really true. Or maybe it's related to short-term versus long-term happiness. I know I should exercise instead of sitting on the internet two hours in a row. I know I shouldn't stay in my pajamas til noon, and that I should send out a few emails. And I really should. It would really be better. So now I know you can know the right thing to do, but still ditch it.
To throw in another philosopher, we can turn to Nietzsche and the Last Man. The Last Man (who I've mentioned before here) is concerned about being comfortable, not being great. The Nietzschean Superman (or Uber/Over Man, if you prefer) knows what he wants and does it. He does not play video games and watch season 6 (?) of Lost back to back. Instead he spends his days perfecting his true life calling, always striving to improve. I need to be a little less Last Man, a little more Uber Girl.