Let's suppose you're normal. One day you wake up and you're thirty. How the hell did that happen? One day your body can handle 200 consecutive meals of cardboard and styrofoam, the next you're embarrassed to have sex with the lights on. Also, you hate your job.
Maybe I'll start a fight club.
So you decide that you can make yourself happier by losing about ten pounds. After all, it sucks to wheeze going up a flight of stairs, and you used to call your abs "The Dictionary"1. So you cut out the burgers and you stop taking the elevator and after a month you've lost five pounds and you feel better about yourself. So you stop cutting out the burgers and start taking the elevator and ... oops.
I'm trying really hard not to see this as a metaphor. Maybe I'll hook up with my girlfriend's mom.
The point is that you can't fix a long-term problem with a short-term solution. If you weigh 190 pounds and want to weigh 170 pounds, then you can't just struggle for a few weeks and leave it at that. You ended up where you are because of the way you live your life. You're eating too much and exercising too little; you weigh 190 because you're living the life of a 190-pound man2. If you want to weigh less, you need to live the life of a person who weighs less.
I'm so deep. Maybe I'll become a Buddhist.
That is to say, if you're not happy with something about your life, whether that's your job or your health or your sex life, you can't just change that thing. You need to focus on what led to the condition that made you unhappy. If you weigh more than you think you should, then why is that? Is it because you're not sleeping enough and so you get home from work and just fall down on the couch exhausted? Or is it because you've been bombarded with unrealistic images your whole life and don't realize that your perfectly normal body is actually perfectly okay.
Feel bad. Then give me money. Maybe I'll buy a really cool car.
Maybe you really are unhealthily overweight, maybe you really do like your job and everything and are adequately healthy but wish you were a few pounds lighter. That's fine. In the end it's better to do things for the right reasons, and to tackle the source of whatever's bugging you, but it doesn't have to be some deep, life-altering experience. Dropping everything and going to Tibet isn't actually a solution; it's just a fancier way to run away.
Maybe next time I'll bring toilet paper.
So why don't diet and exercise work? Well, they do, but only for as long as you keep them up. If you want to see a permanent change, you need a permanent revolution. If you want to weigh less, you need to live the life of a person who weighs less. Your weight will catch up before too long. The same is true of other things. If you want to be happy, identify the source of your unhappiness, the real source, and
1 - Because they were so well defined.
2 - These numbers make sense for a ~6 foot man. So, for women... 140 & 130? I dunno.