I think what Aesop was suggesting is that when you offer a good turn to another human being, one can hope that that good deed will come back and sort of pay a profit to you, the doer of the good deed.
When you expect something of a friend, co-worker, family member, spouse, and they don't live up to that expectation, then you are upset with them, or disappointed.
Imagine a big earthquake strikes California. Would we want people from Mexico saying, "Oh, you can't care for your children-we'd better take them off your hands"?
What leads to resignations is the gap between grads' expectations and the real work situation, according to Wu Chuyin, a commentator at Southern Metropolis Daily.
These findings are in agreement with what you would expect from the evolutionary theory: those who like to make friends and help others can gather enough resources to make it through tough times.
Three months may not seem a huge difference, but according to Dr Christakis it is comparable to the benefit an elderly person can expect from excercising or losing some surplus weight.