When you treat exercise as something 'you should' be doing, you could soon be in trouble.
You go through a cycle of 'being motivated' and start training obsessively. Then you miss a training session and feel bad about yourself. You've failed. After that you punish yourself by exercising more intensely. Of course this cannot last, and ultimately you'll come to a halt again and pretty much stop exercising altogether. Until you feel that motivation again.
I had a client in the past who was training a lot. She lost over 5 stone. I have a degree in psychology and very much use that to my advantage in dealing with clients, but sometimes it's hard to know whether they are training because they genuinely enjoy it so much, or whether it's become an obsession that's going to lead to bad things.
I found out this client tried to kill herself not so long back. Training had become an obsession. No matter how much she achieved, she never felt truly happy.
Important note: Nobody is ever going to be 100 % happy with their bodies. That's just something we need to try and live with. So if you strive for perfection, you'll never get there. Those Instagram babes only show their best sides, and sometimes cry themselves to sleep because they're not 'good enough' (to who?).
In a way my old client's fitness journey was a true success story. She lost all that weight and looked absolutely incredible after having been overweight for so long. But that's of course just the snippet of her best possible fitness achievements. On the other hand it's a tragic story of how any extreme behaviour nearly always ends up in what we percieve as failure. During her recovery she's had to work with really understanding that being as thin as possible is not a route to happiness. Now she's put all the weight back on, and then some.
So when you see incredible weight loss transformations, don't assume they've 'done really well'. It should be so much more important to understand that getting to true fitness and eating healthily should be about feeling better, not worse about yourself.
Only then, even if you're still classed as 'overweight' by the rubbish official BMI standards, you can truly be happy. Just strive to be a little better.
Eat when you're hungry. Chew your food well. Notice how good you can feel after a balanced healthy meal. And how terrible and lethargic you can feel for days after eating too much crap. When you eat better, your body will reward you with more energy and a better hormonal profile, which will automatically lead to a healthy weight as a side product. Focus on adding good things to your diet, not taking anything away.
Weight loss is nothing more complicated than eating fewer calories than what your body burns. Whether you exercise or not, you'll lose weight if you're in a calorie deficit. So use exercise as a tool to feel better -- choose a sport you truly enjoy, or even just get out for a walk to get some fresh air to burn a few calories. Anything helps. And seriously, training less than 10 minutes a day a few times a week can get you in the best shape of your life. Move little and often, and don't use exercise as some sort of punishment. Humans were born to move. I don't believe in wasting your life doing something you don't enjoy (like going to the gym for many people), so choose to do nice things. Try out a new sport, you might love it.
Exercising too much can destroy you. But more importantly, exercising can also truly heal you. Just enjoy it. That's a great start.