Just in case you are ever a missionary. And just in case you are an Elder, because this would never happen to a Sister. And just in case when you are a missionary you move into an apartment and it has a bunch of old phone books sitting around. And just in case that apartment also has a knife in it, that belongs to "nobody" and is clearly against all the mission rules to own or handle. And just in case, while you're sitting at the kitchen table, you suddenly think "Hey! Wouldn't it be a really great idea to take that knife and see how deep into these phone books I can stab it?!?!" Don't try it. Because even though you think it's the best idea you ever came up with, it's probably not. Just ask Elder Hansen.