Answer on @Quora by @RobertFrost01 to Why do the astronauts have books for troubleshooting? – Xochielt Sanchez
Answer by Robert Frost:
No, it wouldn't be feasible to memorize the procedures. Just the two ISS Emergency books total 1363 pages (although some pages are English/Russian translations). The ISS Warning books are considerably longer.
A spacecraft like the ISS or Space Shuttle is massively complex. Operating one requires great care. A stupid mistake can cause hundreds of millions of dollars of damage or even get someone killed. Astronauts and flight controllers are trained to not operate by memory. They are trained so that certain critical skills become automatic and don't require significant conscious thought, but they are also trained to follow the procedures.
Imagine you are in the ISS and a fire alarm has initiated and there is smoke and noise and danger. Quick, can you remember if the CRK is supposed to be deactivated when the CO2 concentration is less than 1.6% or 1.3%? Do you doff the mask when HCl concentration is less than 5 ppm or 3 ppm? Which DDCU do you shutdown to cut power to the Japanese module? On which laptop display can you quickly verify if the Lab IMV is isolated? How about the Node 2 IMV? What's the Tres for a 1mmHg drop in 19 seconds? What happens if you forget to disconnect the ВД (ventilation duct) in the МИМ1 – СУ(FGB) hatchway during leak pinpointing? What order must the three operational controls protecting the crew from electric shock have to be removed or put in place? When isolating ПхО do you power off ППС-21 or ППС-22? How much time is lost when you send the execute command without first sending the arm command?
Not to mention many procedures require multiple people to work together, performing their separate steps in a specific sequence.
Procedures, checklists, and cue cards help ensure people do things correctly when under pressure and greatly reduce the amount of training required.