As part of Lich's Mirror's effect, it typically shuffles itself into your library. If it does, that means that if you'd lose the game *again* immediately after its effect is finished, it can't help you a second time. This can occur in a few different ways. For example: -- You have ten or more poison counters. Lich's Mirror doesn't remove poison counters. If you'd lose the game this way, you'll do what Lich's Mirror says, then you'll lose the game the next time state-based actions are checked. -- Your life total is 0 or less and an effect says that you can't gain life. Since your life total can't be raised, it stays at whatever it is rather than becoming 20, and you'll lose the game the next time state-based actions are checked. -- The number of nontoken permanents you own plus the number of cards in your hand, graveyard, and library is less than seven. When you try to draw seven cards as part of Lich's Mirror's effect, you'll be unable to complete at least one of those draws and you'll lose the game the next time state-based actions are checked. -- You control *but don't own* a permanent such as Immortal Coil with a triggered ability that causes you to lose the game when a certain game state happens (also known as a "state trigger"), and the condition that causes the "lose the game" ability to trigger hasn't changed. If you owned the permanent, Lich's Mirror would shuffle it into your library. In this case, however, it remains on the battlefield and its ability will trigger again.