Well, don't feel so bad. Science says that this feature is built into your brain.
Brain scans have shown that different parts of our brain light up when we're thinking of ourselves versus when we're thinking of other people. That part makes sense -- your brain is partitioned out into separate regions for yourself and for everyone else because you have to look out for yourself first. But where it gets weird is that in some people, when they're asked to think about their future selves, the region that lights up is the one reserved for other people.
"Future Bill can worry about AIDS tests. Now Bill has unprotected sex to attend to."
In other words, if someone asks you to think about what you'll look like in 20 years, your brain treats it as though you're trying to picture some bizarre stranger. Now think about what that means in terms of your ability to fix what's wrong in your life. What motivation do you have to abstain from your 14th peanut butter doughnut today just to help out some droopy manimal in the future? Logically, you understand that you're endangering the person you'll become, but subconsciously, your brain doesn't have the sympathy to spare for that poor slob, and just wants to enjoy the doughnut.