My motivation at first was having a lot of friends in highschool with better looks and better body than me, a fat blob.
When I tried out lifting with a friend for a few months, I found out that low fat% actually enhanced my facial features, with a much more defined chin and cheeks, and also that being strong (especially compared to all my other dude friends) feels good.
Basically I started getting laid like crazy while also feeling much healthier and lighter in my movements.
With time, I ended up settling with a very cute and smart gf and now I just keep going for health and strength.
Fitness changed a lot of aspects of my life for the better, and that's all I need as motivation to keep going now.