Those who have experienced, they become dumb. Not that they stop speaking, but they speak about the methods, they speak about the way. They don't speak about the truth. They say how to attain it, they say how to avoid the pitfalls on the path, they say how not to go astray, they say, “This is the way, this is the direction,” they give you a few maps, road maps, they make you aware of a few signs that you will come across on the road so that you can be certain that you are moving in the right direction – that's all they can do – but about the truth, or God, they can't say a single word.
So that meaning is also beautiful; myein means “to keep one's mouth shut”. It is from these two words: from myein comes mysterion, from mysterion comes “mysticism”.