He makes this observation:
[...]]the idea of immediate compilation and "unit tests" appeals to me only rarely, when I’m feeling my way in a totally unknown environment and need feedback about what works and what doesn’t. Otherwise, lots of time is wasted on activities that I simply never need to perform or even think about. Nothing needs to be "mocked up."I believe him. I also draw a few inferences.
One is that Knuth probably doesn't spend much time working on systems that do their work by intimately coördinating (with) six or eight other systems with very different usage patterns, metaphors, implementation stacks, space and time complexities, latencies, interface styles/languages/protocols etc. etc. etc.
Another is that he probably doesn't spend much time working on problems that are incompletely and ambiguously described (and that can't be fixed in a meaningful time and/or budget), part of an ad–hoc domain, intrinsically fuzzy, aiming or a moving target from a moving platform, subject to capricious and arbitrary constraints, etc. etc. etc.
And thus is the working life of the research computer scientist different from the working life of the commercial software engineer. I'm tempted to say (and so I will) that the jobbing industrial programmer spends more time in an unknown environment and needs more feedback (and, right now!) about what works and what doesn’t more often than a researcher does.