I spent a whole book writing about it, and I am not sure I ever could define it in one handy passage. That is part of its charm. Although the Beach Boys introduced the world to psychedelic music, their record Pet Sounds wasn't that accepted by the large public. Pet Sounds is a difficult and very emotional record coming from a man at an extremely troubled point in his life. The audience was expecting more songs about girls, cars and fun in the sun, not this soul-searching.
Many people look down upon, seeing the musicians as a bunch of stoners.
But they don't realize psychedelica helped rock advance technologically. The psychedelic mindset emphasizes that there are no rules, that imagination is everything. It was an invitation to experiment in the studio, whether or not drugs are actually involved. In the states the psychedelic sound was a bad trip, whereas in the UK it was more optimistic. Tomorrow never knows'.