If we subscribe to the Dreyfus model of skill acquisition, there are five stages to learning and mastering any given skill or profession:

1. Novice
2. Advanced beginner
3. Competent
4. Proficient
5. Expert

Novices follow rules which have been established for them. When the nuclear reactor starts flashing its "meltdown warning light", for example, they quickly reach for the manual and look for instructions. As they progress up the chain to become experts, intuition gradually supplants obedience.

Expertise is difficult to articulate, but they asked some very experienced, expert airline pilots to write down instructions intended to be read by novice pilots. Then they asked the expert pilots to follow their own instructions. The result? The performance of the expert pilots was hampered by having to follow rules...even though they had written the rules themselves.

In most situations, there probably should be a manual, but if you ask a veteran of any trade or profession to follow instructions, you hinder them from being able to do their job well, and they'll be so miserable they'll leave.