https://news.ycombinator.com/item?id=4103417
Two overarching principles here:
1. Sane customers value determinism more than they value maximizing the productivity of a single hour. They're engaging you because they want a thing done, and the order of their concerns is: (i) assurance that the thing gets done, (ii) getting the thing on a predictable schedule, (iii) getting the thing done sooner, (iv) that they're not making a fool out of themselves by paying way over the market for the thing and (v) how much they pay. Note how far down the list the actual absolute billing number is.
2. Conduct a thought experiment: imagine you have a project that is going to take you a week to finish. Now imagine you take 100 Provigils (don't do this) and get the project done in 3 days instead. Who should get the economic benefit of that efficiency, you or your client?