How many times has this happened to you? You leave work, decide that you need to get groceries on the way home, take a cellphone call and forget all about your plan. Next thing you know, you've driven home and forgotten all about the groceries.

Or this. You decide, perhaps circa Jan. 1, that it's time to lose weight; you need to eat less, eat better and exercise more. But by the first of May, your New Year's resolutions are a distant memory.

Human beings are, to put it gently, in a unique position in the animal world. We're the only species smart enough to plan systematically for the future -- yet we remain dumb enough to ditch even our most carefully made plans in favor of short-term gratification. ("Did I say I was on a diet? Mmm, but three-layer chocolate mousse is my favorite. Maybe I'll start my diet tomorrow.")...