One of my friends smokes. He first got started when he was in an underdeveloped market when he was really bored (no internet access and an extremely unreliable electricity grid will do that to you) and found out that cigarettes cost about 50 cents a pack.
When he came back, he started to cut back on the habit. But he didn't quit completely. He would only smoke in social situations, and only with cigarettes that he bummed off other people. Then he started buying his own cigarettes. Went from 5 cigarettes a day to a half pack. Eventually he graduated to a full pack a day smoker.
The way he first started smoking is what really struck me. He was in a foreign country and was really bored. That just boggled my mind. My friend is not a stupid person. Quite the contrary. He's actually very intelligent. But he has very poor self control and apparently his intelligence does not extend to his own personal affairs. Because he's aware of the deleterious effects of smoking and he still does it.
This is a classic example of short term bias. Because any perfectly self interested person would not smoke. And if they were previously irrational and then suddenly turned self interested, they would strive to quit as fast as possible. Because smoking leads to debilitating and fatal diseases such as emphysema, lung cancer, and heart disease. Any person who cares about their life would simply not smoke.
But those diseases and conditions come later on in life. And there isn't a guarantee that a smoker actually gets them. There are a lucky few who can smoke like a chimney and never have those complications. But the benefits of smoking a cigarette in the present, the buzz, the nicotine, and the stress relief are immediate and guaranteed. So that's why smokers keep on smoking. Because they see an immediate benefit while the negative effects occur in the future.
I read a book called Gang Leader for a Day and it was about this Chicago School economics major who embedded himself in an inner city gang for a few years. And in one of the chapters, the gang leader is talking to the author and they're talking about whether it's smarter to buy drugs from a supplier with a discount now or in the future. The author says something like "well it depends on the difference between the immediate discount and the future discount. The gang leader replies with "no, you take the discount now. Because you don't know whether that dude is gonna be in jail or shot or something".
We're hardwired to think in the short term. While saving for the future or modifying your present behavior for future benefit (proper diet, exercise, studying, etc) are relatively new concepts, they are absolutely essential for success in modern society. But we put it off because it's always more immediately gratifying to view yet another lolcat meme instead of studying for a test that's two days in the future.
There are plenty of people who think the best way to educate our children is to immediately reward them for routine things like doing homework, getting good test grades, and attending class. Giving them an immediate short term benefit while also allowing them to gain the long term skills needed to function in the economy makes a ton of sense. It's sort of like tricking them for their own benefit.
This is what humans are programmed to do. And it's important for policy makers to consider our short sighted nature when they try and pass programs for our ostensible benefit.