The Buddha said we already possess that which we seek; we need not look outside ourselves for sources of happiness and of insight. I’ve always felt a little unease at that idea, and I’ve finally figured out why.
An accident occurs and I lose both my sight and my hearing. Will I be able to learn about something I know nothing about? No. I won’t be able to learn about the advancements in Machine Learning or nanotechnology, or grok a new language. But I will still be able to find contentment, avoid suffering to a certain degree, and maybe attain some form of profound enlightenment because of the constraints of my situation.
See, there are two types of knowledge: self-knowledge and worldly knowledge. I would be able to attain all possible self-knowledge if I lived my life in a sensory deprivation tank. I would not be able to attain knowledge about the world in the same situation. For the acquisition of self-knowledge, external inputs are nice, but not necessary. For the acquisition of worldly knowledge, external inputs are critical. Without them, no learning occurs.