[evincarofautumn]

Sure, but I would be equally happy to pay either of you by the hour if you set your rates according to your respective skill levels, because the price would come out the same. Also there is an implicit expectation of reasonable competence.

For example, hourly pay is quite reasonable in jobs that just need a competent body to fill a shift—i.e., where the only “result” you want is “the shift gets filled”. When I was working in a kitchen, I put in the same four-hour shift every time I went into work—prep, serve, clean. If I worked n shifts a week, I got kn dollars that week, fair and square.