First, take a mild hallucinogenic drug, like ecstasy, where your senses are heightened, and you lose the ability to block out all of the external stimuli—sounds, sights, smells, etc.—that you normally instinctively filter out without having to spend much mental energy. Even things like casual social touch can be, at best, jarring and distracting. Suddenly you are trying to block out the conversations of 6 different couples/groups elsewhere in the room, while also trying to focus on the conversation in your group. This becomes incredibly draining, very quickly.
Second, imagine that the people you are talking to are from the same foreign country as each other, so they understand each other, but you would not, so they speak English for you. They typically use the right words, but you struggle to piece together what they are saying. A major problem is that they have a terrible habit of using idioms from the textbooks they used to learn English, but the books were 100 years old, so you do not understand the idioms. If you had the time to sit and read a transcript of the conversation, you could eventually figure out what they were saying. But since you are in a real-time conversation, it increases the mental energy you have to expend to understand them, plus you and they both realize you are really not getting everything they are saying. This compounds the problem that all of the other conversations in the room are filtering into your conversation, since you cannot block it out. Things are getting frustrating.
Third, some linguists tell us that 80% of face-to-face conversation is paralanguage—those nonverbal cues such as tone of voice, facial expressions, and body language, that inform the words that we are saying. However, these foreign speakers are using paralanguage that is different you do not understand, but they all seem to understand each other correctly. The facial expressions that you think mean they are happy, to them actually means they are telling a very serious, even sad story. So even if you were fully able to focus on and comprehend their words, their paralanguage is different from what you expect. You find yourself expending even more mental energy trying to figure out what their tone, facial expressions, and body language means, while trying to mirror appropriate responses. Things continue to get more frustrating, both for you, and for them. At best they think you are “slow,” and at worst, just a rude jerk.
Fourth, you have been expending a lot of mental energy, and are finding it increasingly hard to block out the sensory stimulation. Sometimes they touch your shoulder and you jump, making everybody feel uncomfortable. You try to limit the perceptions coming in by “focusing your attention inward." You look sort-of in their direction but you are not really “looking at them,” and they know it. Partly because you may be looking at their shirt, their pants, their shoulder, their hair, anywhere but in their eyes or at their face. Face-perception is already very difficult for you, meaning, it is very difficult to recognize people by their faces, so you never developed the instinct that most people do to look at people’s faces in a social way. But it also consumes a lot of energy, because the face contains an amazing amount of nerves and muscles, and is always moving to express feelings and ideas. It becomes far too difficult to try to understand facial paralanguage, since it’s “foreign” to you anyway, so you try to “turn off” your eyes and just focus on the words they are saying.
By this point, the people you are talking to recognize there’s “something wrong with you.” In the process of trying to be social, you have completely exhausted all of your mental energy in just 10 minutes. Welcome to mild autism.