Money is not the only motivation for work, because there are people who spend countless hours working in fields like teachers, who are not paid nearly what they are worth. When you choose a profession, the first criteria for the selection is that one must love what they do, or else, you will be unhappy.
Money has a part in the decision, but it is not the only motivation. Another factor is location, how long a commute are you willing to put up with twice a day? If your answer is that you want to work closer to home, then perhaps money cannot be the initial motivator for the decision.
Some people want to work in certain professions and will accept less money in order to gain entry into a certain field.
Money as the only motivation can be proven only in the extreme circumstances where individuals will do anything for money, such as commit crimes, willingly injure people by engaging in immoral activities, or knowingly breaking the law.