The problem with estimates is that it's easy to install (and easy to estimate the time involved installing) a new air conditioner (or water heater or other appl

The problem with estimates is that it's easy to install (and easy to estimate the time involved installing) a new air conditioner (or water heater or other applicance), but it's hard to estimate how long it will take to design/invent a new air conditioner, etc. In software, the frustration between customers/management and developers comes from this misunderstanding. They think they're asking for a simple install of a thing (which has known risks), but they're often really getting the invention of a brand new thing (with unknown risks). So my solution is to only give high-confidence estimates for things I've already done once. (e.g. I know it takes me 4 hours to assemble and ship one of my robots. I know because I've done it 100 times. But I have no idea how long it will take to design a new robot using unfamiliar parts from scratch.) But I do try to clearly point out where things are "installations" and where things are "inventions", with the appropriate margin-of-error for each kind of task in the estimate.