It's going to be different for everyone, probably. For me, it was always stuff around networking, systems administration, DB administration, and compiling/link

It's going to be different for everyone, probably. For me, it was always stuff around networking, systems administration, DB administration, and compiling/linking. A tiny example might be something that uses a symlink or, worse, is hard-linked from multiple places. A newbie might not even know that such things are possible; and if you don't point it out or use the terms, they can end up be horribly confused.