This is a fun way to think about it. A more "economics" way is that you value your time more when you have less of it, so you might sell the 9th hour at a highe

This is a fun way to think about it. A more "economics" way is that you value your time more when you have less of it, so you might sell the 9th hour at a higher price than you'd sell the first. And that's why workers in many industries require overtime. As a freelancer, something I think about is this: I have 3 ways to raise my income: work more hours, bill more per hour, and hire people to work under me. Option 1 is pretty limited. Option 3 is attractive, but brings a lot of headaches, and if I have employees I have to sell enough projects to keep them all busy. The most appealing personally is to be the best I can at what I do, to justify a higher rate.