The worst advice I’ve ever gotten is to go ahead and pursue a potential romance with a friend, because you really can’t ruin a good friendship that way.
It’s not true. You really can. It doesn’t mean you will, or that if you do, the decision was a bad one. But it’s not true, and you should go into such a situation knowing that whether the friendship will come out intact is dependent on a lot of factors, and they aren’t all under your control. Even if it’s intact, it might be quite different — better, worse, who knows? It might need a break for a while and then come back stronger. But don’t go in thinking there’s nothing to lose.
I remembered this advice (which was given to me in college, naturally) this morning because I was thinking about a situation where it might apply, and ended up shaking my head, remembering exactly how not true it is.