That would depend on each person, as an individual. Each person has their own life's experiences and sometimes can relay those experiences to others, as sharing, per se.
Sustained 'motive' can be achieved through desire to achieve one with oneself. Your 'motive' or 'why' you do something is usually based on whether or not, you have any sort of ambition.
Myself, my love for humanity is what drives me to share my experiences and knowledge. The feeling I receive from providing clarity to others fulfills my own individual purpose, which I set for myself.
To be honest- if you have no purpose in your life that can help change society as a whole, you might want to re-consider why you live. Your individual ability to satisfy your own unique purpose can sustain a loving feeling you cannot find anywhere else.
How do you do that? Make the conscious decision that your life is going to mean something more than just simply living.
At least, that is my opinion. I hope that helped.