This is a common feature of how humans work and it is backed by volumes of research. Motivation consists of two types: internal (or intrinsic) and external. Ex

This is a common feature of how humans work and it is backed by volumes of research. Motivation consists of two types: internal (or intrinsic) and external. External is what you do because somebody will reward you, usually with money. Internal is what you do because you love to do it. In this particular respect, motivation in most people is a zero sum game. If you do something because you love it, and then someone starts paying you for it, the degree to which you do it because you love it must decrease. That's why many people who love to do something so much they decide to go get paid for it gradually find themselves not liking at all what they used to love to do.