Concentrate on the yellow wall, mind.
TL;DR. Food for thought. Can a monk's true ability to control his mind be tested under the influence of recreational drugs? Our mind is an ever-wanderer. The minute you think, hold on, I'm just going to sit here and think about one thing, and one thing only, say the yellow wall in front of you, your mind just won't let you. For the first minute or so, you think of just the yellow wall, you see, you start to immerse yourself into it. Except then, suddenly your mind remembers a tune from Coldplay's track and you start humming. No. Brain. Shut up. We're concentrating here. Not the yellow song. Yellow wall, that's it. You go back to just the yellow wall, except this time you're sure nothing can distract you. You're trying to discard all triggers from sensory events that remind you of yellow. But then! The fridge starts it cooling cycle and it suddenly becomes louder than usual. Yellow. Mind yellow wall. Fridge? Agh. Yellow. Oh wait! I have a m...