The best reason ever [simply] articulated imho was in Warren Ellis' [sadly yet to be completed] Doktor Sleepless -
Q: "What do you think you're going to learn?"
A: "How to permanently change my mind. Because the one I've got isn't big enough."
In Ecuador’s Rain Forest, Indigenous People and Inner Life - NYTimes.com:
"All appeared normal, until after what seemed like 20 minutes it no longer did. A montage of images emerged from the darkness — neon crystals, a lion. Soon my body dissolved into the surroundings, swallowed by a sea of energy. Unmoored and disoriented, I was adrift in a more expansive reality.
This brought a greater awareness, and I began to perceive things that had been imperceptible, like a low-frequency vibration permeating the environment. The hum of the universe? My thoughts drifted between visions. I imagined myself basking in the sun on the flanks of the volcano Chimborazo. I saw images from childhood and of random friends back home, all presented like scenes from the narrative of my life. Then my father appeared, seated in a chair before me, like a ghost. For several minutes we exchanged the sentiments that I had regretted not expressing before he died: What a life we shared, we both seemed to say. I looked down and noticed I was sobbing, and when I looked back up, he was gone."