Finding an exercise I liked.
I was that kid who fakes notes to get out of PE, I have never done any kind of sport, hate swimming etc etc
Then at 31 I got together with my now husband who was a runner. I was always the person who was like 'ha ha I don't even run for the bus!', but I wanted to get in shape for our wedding and he encouraged me to do couch to 5k. I LOVED it. I lost 18lb without even trying and it has stayed off since.
I don't know what it was really, but it just clicked - the freedom to just stick on my trainers and go anywhere at any time, for ten minutes or two hours. To put on banging tunes or a podcast or just listen to nature, I loved it all. Ten years later I've carried on running through having three children and an autoimmune disease, I've done loads of 10k races and parkruns and three half marathons. I will do a marathon one day.
It was the only thing that worked, I can't do diets but I run 3-4 times a week and that keeps me in ok shape, I couldn't live without it.
So I say, anyone can find an exercise they love - it might be fencing or rock climbing or something obscure but there will be something and you will stick to it because you love it. Try everything, you only get one life and one body, so find something it loves .