Humans are great short term thinkers, and pretty poor long-term thinkers. We want things and we want them now. This makes things like paying down old debts, saving for the future, and cutting carbs oh-so-tough. Not paying debt and eating pasta is just...better than the alternative. At least, until a few years later when we’re cursing our younger selves and trying to repair the damage that was done.
A big part of this reason is that in essence, we’re actually of two “brains” here - an emotional (short term) brain, and a logical (long-term) brain. As one author of a study on economic behavior said, “Our emotional brain wants to max out the credit card, order dessert and smoke a cigarette. Our logical brain knows we should save for retirement, go for a jog and quit smoking.” Even the most logical among us has felt this tug, and it’s telling to know that we’re really hardwired to respond to short-term stimuli. Flashing lights, great sales, oncoming tigers.