Earlier quoted context omitted.
You might have forgotten them, but there were also books printed on paper.
H4x0r doesn't need book. H4x0r try 4nd err0r. Books were just knowledge. Debugging was skill. At certain point in knowledge-gain, you develop a good skill and after that point, you don't need books anymore. Maybe from time to time. I still have a suse6 printed manual.. I can't see it in the cellar, but It've been HUUGE
If you have access, why would you debug machine code without using the reference manuals for a particular processor and OS and whatever else you're dealing with? You could spend hours chasing a "impossible" problem that could be easily be found in the errata for a giving stepping.