That's true, but the way you described it makes the difference between a professional commercial photographer and a professional art photographer pretty insignificant. In both instances, if you fail to produce work that pleases the people who pay for it, you won't get paid. It's very rare to find someone who makes a living from uncommissioned art photography alone.
Most amateur photographers - as in almost all of them - will never sell a print.
Most amateur photographers - as in almost all of them - will never sell a print.