The easiest way to explain it to people that ask me is: “I train because I can”
I started training 1) to gain muscle, and 2) to gain strength. This is not unusual, if you’re a man, but I still don’t find too many women who are interested in packing on 20 pounds of muscle. I was a skinny little ectomorph, 107 pounds at 5’7", and gained some 25 pounds of muscle in the first 12 weeks I lifted.
Now, I care about 1) functional strength and overall fitness, 2) long-term health, and 3) appearance. My immediate goal is to shed some fat. I never had this problem when I started lifting. I just don’t burn off the Haagen-Dazs like I used to. 
College Football
aesthetic to a point
separate myself from others
in a few years (4 or 5) looking to compete in the NY strongman contests
Also live to 100 years of age (I’m 18 years old now, so that may fall under a long term goal)
A number of reasons in no particular order, health, I enjoy it, it humbles me (I need that at times),look good, gotta do something, can do it at home.
Why do others think:
I have a “great physique”?
I’m a talented guitar player?
I’m a skilled programmer and know more about computers than any one man should know?
I’m just one generically smart motherfucker?
(Read on, this isn’t a vain post, I swear! 
)
Because I think I’m a sad pathetic loser who hasn’t even scratched the surface of any of the above, that’s why.
The day I feel I’ve furthered myself ‘enough’, I will have no reason to live anymore. Why bother living if you’re not going to fucking do anything?
That’s my take on things anyway.