> Programmers only come in when the automatable parts of the system need to be implemented, and work from a detailed and precise spec.

A lot of systems are complex enough that you can’t get to that stage (and if you think you do, think again). Mostly because of communication issues and time concerns. Which is where the agile manifesto comes in and recommends the talk-do-show in short cycle. It needs not to be hacked together and the showing helps with communication, the talking guides the doing, and the doing is what pays for everything.