This isn't really true for all software development. If you write a detailed design, the process for writing the software is as simple as "write what the design says you should write, then test it conforms" It's only true for the sort of software development where you design while you write, AKA hacking.

I'm not against hacking per se. I'm doing it right now. But to take it as the de facto way the software industry functions is wrong. Hacking has certain problems, like unanticipated problems tend to stall the process (My own recent encounter had me blocked for three days, trying to think of an adequate solution to the problem of how authentication should work in an environment where HTTP servers and clients are essentially "decoupled", that is a solution to the problem of where presentation and application data are coming from two different sources, how does the data provider verify the presentation logic is trustworthy? It's a hard problem to which I have only a partially satisfactory answer... but I digress.)

The process for writing code tends to be unwritten, simply because in the best case it is so trivial that writing it is an insult to the reader. I guess the industry's collective problem is that the best case happens so seldom.