What does "rationality" signify in this case? Unconsious co-ordination and control of the senses and muscles? That is not what I, or any sane person, understands by the word "rationality"! Is "rationality" just a universal signifier for "doing stuff right"?

No, instrumental rationality is the meta-process you apply to choosing or refining the primary process (i.e., the actual toast-buttering).

If you look carefully at the original statement that I made, you'll find that there are a large number of places where people fail at instrumental rationality:

• Failing to establish success criteria in advance
• Failing to determine desired/feasible levels of investment
• Failing to test
• Failing to generate alternatives
• Failure to apply creativity
• Failure to apply problem-solving

And these are just the failures you can generate by a literal reading of my statement, without addressing things like failures within each of these areas, like failure to establish a baseline for testing, etc.

These are all ways in which I've seen large, expensive, real-world projects fail... and a lot of people in the business world will nonetheless look at you funny when you ask questions like, "so, how will this make the company money?"

(And a small minority, thank heaven, will think you're a genius (or recognize a fellow-traveler) and start bringing you in to ask these kinds of questions sooner in the process.)