Adopted from the following great saying of Dan Ariely from his book Predictably Irrational..
“To summarize, using money to motivate people can be a double-edged sword. For tasks that require cognitive ability, low to moderate performance-based incentives can help. But when the incentive level is very high, it can command too much attention and thereby distract the person’s mind with thoughts about the reward. This can create stress and ultimately reduce the level of performance”