This was in response to your original comment that got flagged:
There's a few ways it can do so.
1. Depression: if life itself feels pointless, why care about your health?
2. Environment: lots of snacks, lots of work, little free time can add several kilograms.
3. Upbringing: if all you did in your high school and university life was hang out with friends and play computer games or generally un-athletic activities, the habit and drive to keep pounds off is absent.
4. Stress: if you're dealing with a really hard project at work or school, you may "put off" exercise and eating well, in order to give you time to finish it and comfort for the hardship. And when you do get some free time you may want to just lie around.
5. Money: if you're poor cheap snacks and unhealthy but high calorie meals are readily available at almost every corner of your city or town. There's no place in my downtown area where I can grab some roasted vegetables quickly to take back to the office. The salad places are expensive and also have high calories from dressing and lots of nuts and cheese.
6. Disorders: addictive personality being the foremost in my mind. If it feels good, keep doing it. Even if you don't need it. Even if you're almost full to bursting.
There's more I'm sure, but those are off the top of my head.
That gripe is different from what I responded to. You originally said it's unfathomable how someone could get 100 pounds out of shape, and I listed a few ways that it can easily happen.
It sucks your original comment was flagged - I can see how people may have thought it was a bit harsh, but it was true. You don't see how it can happen.
Speaking only for myself, it's simple: I'd never known anything different. I'm 6'2", and was ~230lb when I graduated high school. On January 9th of this year I was 318lbs, and decided to make a change.
I'm 285lbs now and still dropping a few pounds every week. My clothes are starting to fit poorly, I've had to adjust my watchband twice now, and my wedding ring will barely stay on my finger.
I hit 100 lbs. overweight after Hashimoto's destroyed my thyroid. Now, on thyroid meds, I'm about 20 lbs. overweight, but it's hard to maintain even this. If I'm not careful, I can gain twenty pounds in a month without batting an eye. I've yoyo'd several times since being diagnosed.
There's a few ways it can do so.
1. Depression: if life itself feels pointless, why care about your health?
2. Environment: lots of snacks, lots of work, little free time can add several kilograms.
3. Upbringing: if all you did in your high school and university life was hang out with friends and play computer games or generally un-athletic activities, the habit and drive to keep pounds off is absent.
4. Stress: if you're dealing with a really hard project at work or school, you may "put off" exercise and eating well, in order to give you time to finish it and comfort for the hardship. And when you do get some free time you may want to just lie around.
5. Money: if you're poor cheap snacks and unhealthy but high calorie meals are readily available at almost every corner of your city or town. There's no place in my downtown area where I can grab some roasted vegetables quickly to take back to the office. The salad places are expensive and also have high calories from dressing and lots of nuts and cheese.
6. Disorders: addictive personality being the foremost in my mind. If it feels good, keep doing it. Even if you don't need it. Even if you're almost full to bursting.
There's more I'm sure, but those are off the top of my head.