[Question] What are the unwritten rules of academia?

I came across this tweet a few minutes ago, and it got me thinking about how much of academia is gatekept by unwritten rules and rituals. Are there any good resources out there documenting such rules for outsiders? If not, this seems like a worthy task to attempt for anyone with such knowledge.

Are there any aspects of academia or of doing original research that you would not have known about if you had only learned through textbooks? With my current position of learning exclusively at home without a mentor, I worry that I may be missing many of these unwritten rules, and don’t know how much of a disadvantage this places me at.