(It can be "hard" to do because it can be an uncomfortable or "boring" thing to do, that you don't really want to do. But if you just do it anyway, it's "easy", it doesn't take any skill, anybody can do it, you just have to do it. It is sort of a kind of exersize for your mind, like going to the gym for your mind. You are practicing: a) noticing what your mind is doing, self-reflection in the moment; and b) directing your attention).