My guess is that most of think of giving as a one for one or 50-50 split. In other words, we give about as often as we get. We may get a bit out of balance one way or the other at times, but we average the 50/50 ratio over the long haul.
Trouble is, that's really not nearly enough.
Giving is a form of priming the pump. If you ever had to pump water from an old fashioned pump you know you'd have to really work at it, moving the handle up and down before you'd get any water.
But once the water began to flow, you wouldn't have to pump very hard at all. You had to "give" at the beginning so that you could receive.
Life is a lot like that old pump. People respond to giving, but it takes time, and it takes more than giving "your fair share." The 50/50 formula just won't work.
Here's the secret: the more you give, the more you end up getting in return, either in actual benefits (someone actually gives you something) or self-satisfaction in knowing you made an impact on someone else.
Giving primes the pump. We end up the greater recipient.