Over millions of years, evolution selected strongly for creatures that lived largely in the moment. In every species that's ever been studied, animals tend to value the present far more than the future. And the closer temptation is, the harder it is to resist. When we're hungry, we gobble french fries as if driven to lard up on carbs and fat now, since we might not find any next week. Obesity is chronic not just because we routinely under-exercise, but also because our brain hasn't caught up with the relative cushiness of modern life. We continue to downplay the future hugely, even as we live in a world of all-night grocery stores and 24/7 pizza delivery.
Future-bashing extends way beyond food. It affects how we spend money, why we fail to save enough for retirement, and why we so frequently rack up enormous credit card debt. One dollar now seems more valuable than $1.20 a year from now. Doctors find that many people who've had heart bypass surgery don't take all the measures they recommend to significantly reduce the odds of future cardiac complications. The allure of that juicy pepperoni pizza now is too much to overcome against the distant benefit of living longer. So the more we minimize the future, the more we go for drugs, booze, and gluttony.
GOOGLE IT: This bias is also called “The Hyperbolic Discounting Curve.” The curve gets steeper and steeper as the reward date is pushed further out into the future. This makes it hard for people to make the right choices today for goodies that are years away.