When we do not understand the nature of self, we may be fearful when we hear Buddhism proclaim there is no self. When Buddhism teaches that there is no self, it is just like saying there is no fist. Buddhism is asking us to look beyond the concepts and ideas of self and realize the activity from which self arises and disappears. Imagine hiking in the mountains. We come around a ridge and suddenly, surprisingly, we see a magnificent vista.
Some religions posit a witness, an observer, independent from the activity.
Buddhism rejects this idea - defines it as delusion. The teaching of no self means that the activity of experiencing is selfless. In extraordinary experiences, such as seeing a magnificent vista, this may be apparent. But the teaching goes further. It tells us that the foundational activity of all experiencing is selfless.