It is saying in India "Keep giving, it will return to you". We Indians like to share things even if they are not sufficient for our own. And what to say if someone has pulled you out from trouble "we will surely try to benefit him in some way".
I am not here to get my piece from someone else's things but to get a receipt that "I have made someone's day" :-)
Someone buying coffee for you sending a signal that the buyer is happy with my efforts. And being recognized as one of the "most awesome feelings in the world"
-Imran Sayyad