The first two, or three, maybe 5... seconds are the base, it's key what happens in the interaction right after the entry point. The biggest disadvantage is that when something important doesn't work, their supervisor, is calling your supervisor, and that can get really.... like little street fighter sometimes. Be friendly and understanding (here you need to act), but that's all you can do. Be honest, and not acting, when the user destroys their device by their own fault, then there's the battle.