The National Institute of Health researched uncovered a neurological paradox which revealed that; throwing money into the mix diminishes altruistic motivation and introduces unexpected behavior.
The results of two separate experiments lead to the discovery that the pleasure center (nucleus accumbens) of our brain and the altruism center (posterior superior temporal sulcus) of our brains are physically unable to light up at the same time. (Popov, 1997) The pleasure center is connected to drug addiction, sex and monetary incentives. The altruistic area is related to our social interactions and forming bonds with others.
In other words, if I asked a friend to help me move my fridge they might whine a bit, but they will probably say yes. If I offer the same friend $20 bucks to help me to do this on a Saturday afternoon they will probably say no and tell me that there are movers for hire who do this.