Here's how the mushroom idea first came up in the context of Western dharma. The mushroom metaphor itself is, of course, an old standard. But this exchange with Bill is why we now talk about the "mushroom culture."
After my 1991 three month retreat at Insight Meditation Society in Massachusetts, I returned home to California and gave Bill my report. It took a couple of hours. Bill sat through it patiently, listening carefully, and only occasionally falling asleep. When I was finished, Bill went through it again quickly, identifying the stages of the progress of insight. I was amazed that he could so easily map my experiences onto the ancient model of development, and annoyed that I was hearing this for the first time. Surely my interview teachers at IMS had also known where I was on the map and had withheld the information from me. I complained about it to Bill. Why did they withhold information that could have been useful to me?
Bill said, "They treated you like a mushroom."
"What do you mean?" I asked.
"Kept you in the dark and fed you shit," Bill said.
The mushroom metaphor became my personal shorthand symbol for the secrecy and paternalism that was the de facto code of conduct for many mainstream Western dharma teachers at the time. I was angry about it, at times enraged, often indignant. All through the early and mid 90s, I ranted about the mushroom effect to anyone who would listen. One of my closest friends and confidants was Daniel Ingram. I told him about the secrecy, the taboos, the paternalism and the withholding of information, and my view that this culture of willful ignorance was holding students back. Daniel and I laughed about Bill's off-the-cuff mushroom comment. Daniel was not yet a regular meditator, and had not yet met Bill Hamilton or any of the other celebrated meditation teachers, but he was a good listener and was fascinated by this odd culture of secrecy that seemed to fly in the face of otherwise well known and accepted methods of pedagogy. A few years later, Daniel encountered the same taboos when he began meditating intensively and sat his first retreats. Now he and I had even more fuel to complain to one another about the asinine secrecy and paternalism of mainstream Western dharma and together we further developed the idea of the mushroom culture, mushroom factor, and mushroom effect, etc. Daniel wrote about the mushroom culture in MCTB. The public response was electric. The mushroom metaphor struck a nerve with a whole new generation of meditators who shared our distaste for paternalism, secrecy, and creepy, outdated religious taboos.