Dave is right,
you need to enjoy what you do and provide value to people (and helping others is one of the most enoyable things to do).
The point is that you arre intrinsically motivated to do thinsg you enjoy or work for a purpose you believe in. Making yourself sweat and strain doesnt get you anywhere although society likes you to think thats the way. imho any time you feel negative there is somethingw rong with what you are doing so hard or unenjoyable work is not the way.
Studies have actually shown that beliefs can turn genes on and off btw. You might be supirsed how little the physical limits of form actually are.