At the end of a day with an agent, you know what shipped. What you usually don't know is what it cost you. How many hours went to each client or project? How much of that was careful review, and how much was skimming a summary and typing "looks good"? How much focus do you have left for the afternoon?

Guessing doesn't work here. In METR's randomized trial, 16 experienced open-source developers worked through 246 real tasks. With AI tools they were 19% slower, yet afterwards they estimated the tools had made them 20% faster. When agents do the typing, your own sense of where the time went is the least reliable number you have.