What is it that motivates an employee to reach peak performance?

The answer usually given is 'employee satisfaction'.

However, that is hard to measure.

A person may be dissatisfied because he wants to do a better job and wants to improve his own work and that of his group. He wants to do bigger and better things. He may feel he is being held back.

'Responsibility' – not satisfaction – is often the answer.

Responsibility cannot be bought with money. Financial rewards and incentives are, of course, important but they sometimes work negatively. They work only where other things have made the worker ready to assume responsibility.

Nothing challenges  persons so effectively to improve their performance as a job that makes high demands on them.

The way to do this is to give employees the information needed to measure themselves and the opportunities for participation that will give them a managerial vision.

This does not mean management should drive people. On the contrary, management must let them drive themselves by focusing their vision on a high goal.

Source: The Principles of Management, Peter F. Drucker