If you really want to motivate humans, you need to do these two things: make it personal and make it purposeful.
Personal: When radiologists were shown a picture of the patient along side every CT scan they interpreted, they were much more likely to notice things that were wrong with the patient.
Purposeful: When hand-washing stations in hospitals had signs reading "Washing your hands keeps patients from getting sick," they were more likely to wash their hands than if the signs read, "Washing your hands keeps you from getting sick."
The more I read, and the more I compare it to reality, the more I'm beginning to see the centrality of relationships to humanness.
I used to see life as competition, and that the most powerful motivator was self-interest. And I thought this was good--that it made us stronger, more creative, harder working.
But as Daniel Pink Pointed out in Drive, and as he pointed out in different ways in To Sell Is Human,the opposite is true.
If you really want to optimize human motivation and performance, you need to tap our pro-social instincts.