[PubQ] Unspoken rules in the publishing industry

So, I've been stalking this sub for a little over a month now, and I've seen a few comments on various posts mentioning some unspoken rules in publishing culture. For example, "Never approach your agent's colleagues directly; only communicate with them through your agent."

Apparently, this rule is never explicitly stated unless you happen to break it—or one of the countless others I’m likely unaware of. This concerns me, as much of publishing culture seems vague and far from intuitive.

Could everyone here share their experiences and insight into the many unspoken rules to help newbies like me stay out of trouble?