The problem is never dealing with the things you have to do today -- It's dealing with the things you don't. Whether it's things you need to do sometime in the future, or things that you may never need to do at all, or the things that you want to do.

For me, keeping track of the three things I'm doing today is far less of a problem than making the decision what those things are, and in being able to file things away so I can say to myself (and to others), "If it's important, I'll deal with it (and won't forget that it exists), but for now it's not my top priority".