It's hard to express in words because words are the messenger and contact is the message. Human experience is so complex. So many things running in the background become part of who we are. Behavioral scripts. Memorized personalities. The disturbing, continual sensation of hormones pumping into the body. After a certain stage in one's life pure awareness is no longer possible. As you find yourself, you cease to be able to truly imagine what it's like to be another human being--so many of your own memories, connotations, thoughts and feelings get in the way. You can simulate another person's awareness only through the lens of your own psychological and biological biases. Your experiences as other people are mere copies of your own image, housed in your own consciousness.
A single human's sphere of perception is unimaginably vast. It's hard to get an idea of its size until you spend long enough in solitude--only then does your sense of self expand, ever and ever larger, until you no longer realize that you are there. A lone human being is a disembodied consciousness, its immediate environment a mere extension of itself. When one spends several weeks in a single building, distance ceases to have meaning. You are sitting at your desk and you are eating in your kitchen. You are watching television. You are reading. The house becomes your body. You are but a voice, and everything outside is the product of your imagination.
Interacting with another person after an experience like that is jarring at best. Impossible, even. The human brain is wired to perceive other humans as mere objects in a sensory environment. To be able to see into another person's mind, and read not only their thoughts, but their concurrent daydreams, their residual stress over losing their wallets, their squirts of lust-cravings, their irrational fear of snow from a traumatic experience in childhood--to see another you, not you yourself, but a creature of identical capacity for awareness, born from the same mold---it's too much. True telepathy would drive people mad.
Each of two different people can experience the same event and tell a completely different story. Have you ever wondered why?
Extend that to sex--the ultimate form of human contact, in which two conscious, aware human beings unite as one being, forming a closed system--and I wonder why people's brains don't explode mid-coitus. (Explode boom, not explode unf.)