When we began the one-year retreat, Gen Lamrimpa told the meditators: You may be visited during this year by demons, especially if you're progressing well in the practice. There are many traditional accounts of this; it's part of the territory. You learn how to deal with them, how not to succumb. The very engagement with them is part of the practice. In a sense, you need them. The Tibetans take this very seriously.
— B. Alan Wallace, The Four Immeasurables