Moving from a technical role into a supervisory one

The move is usually offered on the strength of technical performance and then judged on something else entirely. The first year can feel like a demotion: you are slower at everything, the work you were good at belongs to someone else now, and your results arrive through other people. Some people make the move and want to go back, which is a legitimate choice rather than a failure. If you have made it: what was harder than expected, and what would have made the first year easier?