"Of greatest significance to me has been the insight that I attained as a fundamental understanding from all of my LSD experiments: what one commonly takes as 'the reality,' including the reality of one's own individual person, by no means signifies something fixed, but rather something that is ambiguous—that there is not only one, but that there are many realities, each comprising also a different consciousness of the ego. One can also arrive at this insight through scientific reflections. The problem of reality is and has been from time immemorial a central concern of philosophy. It is, however, a fundamental distinction, whether one approaches the problem of reality rationally, with the logical methods of philosophy, or if one obtrudes upon this problem emotionally, through an existential experience. The first planned LSD experiment was therefore so deeply moving and alarming, because everyday reality and the ego experiencing it, which I had until then considered to be the only reality, dissolved, and an unfamiliar ego experienced another, unfamiliar reality. The problem concerning the innermost self also appeared, which, itself unmoved, was able to record these external and internal transformations. Reality is inconceivable without an experiencing subject, without an ego. It is the product of the exterior world, of the sender and of a receiver, an ego in whose deepest self the emanations of the exterior world, registered by the antennae of the sense organs, become conscious. If one of the two is lacking, no reality happens, no radio music plays, the picture screen remains blank."
—LSD: My Problem Child, 1980 Nov 15