Sometimes we put our glasses in our pockets or on our heads and later we ask, "Where are my glasses?" This is quite common. We look everywhere else without finding our glasses. That is why we need the guru, who can say to us, "There are your glasses." That is all that the Mahamudra and Dzogchen teachers do: they simply point out. What they are pointing out is something that you already have. It is not something that they give you. They do not give you new glasses. They cannot afford to give you new glasses, but they can afford to point out where you can find your own glasses.

When we receive pointing-out instructions from our root teacher, we are being introduced directly and nakedly to the reality of mind's nature. These instructions become very effective if we have prepared ourselves to receive them.

...Pointing-out is similar to pointing to the sky when it is very cloudy and saying to someone, "There is the blue sky." The person will look up and say, "Where?" You may reply, "It is there, behind the clouds." The person to whom you are pointing out the blue sky will not see it at first. However, if even a patch of blue sky appears, then you can say, "Look--the blue sky is like that." The person then gets a direct experience. He or she knows experientially that there is blue sky, which will be fully visible when the clouds are gone.

--from Mind Beyond Death, by the Dzogchen Ponlop Rinpoche