Something I've been thinking about a lot lately is the will to win. What separates the best from the rest? I think that it's the will to prevail rather than to make any assumptions.
For example, look at Gata Kamsky. He gets into drawish endings where he has the slightest of advantages and then he just keeps pressing until his opponent cracks. Sometimes that gets him into trouble, such as yesterday against Tomashevsky in the World Cup, but more often than not he doesn't crack under the pressure and he converts an awful lot of those positions.
Now it's easy to say that Gata is a veteran and that's why he has developed the ability to press on in those positions.
Then yesterday I'm looking at a game from when Magnus Carlsen was a twelve year old IM. He has the White side of a Berlin and he heads right into the endgame line with the annotators noting that even at that young age Magnus was well content to get into an ending with a slight edge and just grind away.
Sometimes I like to think that I am developing that ability myself. But then you only need look back a few weeks to this to see that I haven't fully developed this ability.
I think that this will be a rather important next step in my improvement. It's not enough to say you want to win, you actually need to go fight to make it happen.