It's a feeling you get when you've worked your ass off at the gym and later someone gives you a compliment.
It's basically a feeling you get when you've worked hard to achieve a goal and people eventually notice.
The clothes you were about to throw out suddenly fit in all the right places and look amazing on you.
When all is said and done, you do need to put some effort in all that you do, to arrive at a place where people notice a positive change in you. Change then begets compliments and compliments get you to push harder and so the cycle begins.
For some it can become an addiction for perfection. This can become dangerous and lead to anything from an obsession with building your body all the way to anorexia.
Folks, I'm pretty sure you already know but it never hurts to get a reminder that balance is everything.