How do real crackers learn?

I'm talking about the kind of crackers who penetrate in systems, create zero-day exploits and the like. I never met one (obviously!) but I wonder how do they learn their stuff. Do they read deep tech stuff regularly? I assume they already known all the internal details of whatever system they are trying to crack (e.g., TCP/IP, ssh, HTTP, Linux, etc.)... I guess they learnt that stuff at some point in the past and then moved on. Moved on to what? I suppose they stop 'reading' and started to 'produce'; they don't learn from others, they are the source of knowledge for some topics (I mean, a zero-day exploit is something that cannot be learnt... one must come up with it based on previous accumulated knowledge).

I guess I won't ever be able to know how real "crackers" learn by just searching on the internet... but since HN, perhaps you guys know a guy that knows a guy that actually knows how real crackers learn. Would be interesting to read that!