The whole life-cycle thing in general.
Not that I see anything wrong with it, it's just that you'd be amazed at the number of people who start working on large ASP.Net projects before understanding it, rather than vice versa. Hence, it becomes a gotcha.
Note that I said large projects: I think the best way to come to terms with the life cycle is to work on a few smaller projects yourself first, where it doesn't matter so much if you screw them up.
