Imagine you're born on a planet, filled with other humans. Only these humans communicate chiefly through releasing certain scents. You don't know this. You are you as you are, with your ways of thinking and communicating and being. You grow up on this planet being yourself, talking to the other humans just fine, being perfectly polite, but everyone is angry at you all the time.
"How are you?"
"How dare you! You're so rude and arrogant!"
You grow up like this and you have no idea what you're doing wrong. You ask people why they're angry and they just get angrier.
"If I have to tell you what you've done wrong then you obviously don't care! You should know!"
You get fed up of always being in the wrong, being a loner, never fitting in. You start paying extra attention and one day you come to the realisation that certain responses or certain topics come with a certain scent. You begin to suspect there's a whole method of communication you're missing out on, and maybe it's even more important than the actual words you use.
You start consciously noting what smells come with which feelings. You notice that when someone is sad there's a smell of lilies. When they're angry there's a smell of cinnamon.
You realise with horror that you've been going around emitting the scent which indicates contempt or arrogance.
You realise that there's this whole other method of communication which all the other humans do "instinctively" which means they do it without thinking, and they expect you to do the same. They can't tell you what scent means what because they don't consciously pay attention to it. Worse, they won't believe that you don't know because to them it's as natural as breathing.
You start experimenting. You realise you are capable of emitting chosen scents as well. So you observe, you try to figure out which scent means what and then put it into practice, emitting what you hope are the right scents at the right time. Sometimes you get it right, more often you get it wrong.
As time goes by you realise it's more complex then you thought. A scent that's mostly cinnamon with a hint of lilies means someone is newly bereaved. Good lord, this is so much harder than you realised. You've gotten the basic emotions down but that only makes it worse. People see you understand the basics so they're even less likely to believe you don't understand all the far more complex mixes of scents that indicate anything from arousal, to pride mixed with humility, to conflicted joy and all the other complex range of emotions these people can have.
Eventually you get to a point after years of trial and mistrial, heartache and unnecessary upset, where you can pass for normal, where most people won't realise you're "different".
The problem now is that these interactions are exhausting. You have to consciously note all the different smells and match them up with the right feelings and implications, while also consciously trying to emit the correct ones yourself. All the while the other humans do this without thinking, it takes nothing out of them.
You spend your days constantly bombarded by scents you have to make sense of. You meet up with a larger group and it's even more exhausting trying to keep track of everyone's scents. The more people, the harder the job and the more exhausted you are afterwards. The more time you need on your own afterwards recovering your energy.
Imagine also that every sound on this planet is three times louder than every sound on earth. You go for a night out and it's utterly overwhelming. You're supposed to keep track of every scent and emit the right ones while the boom of the music is like holding speakers to your head with the volume as high as it will go. You have to look happy too or people will constantly ask you what's wrong, or get angry with you because you don't look like you're enjoying yourself. You have to correctly analyse everything when you're just so overwhelmed it's barely possible to even think.
Sometimes you manage it and make a good showing of yourself. Sometimes you don't and it just makes the other humans dislike you because you're not talking enough, you're no fun, a bit weird, a bit quiet. And every time you get invited out somewhere loud and busy it's a fight between wanting to be social and have friends, and trying not to be overwhelmed and make people dislike you more because you're not present enough, not interesting enough, not emitting the right scents or correctly interpreting other's scents.
This is what it's like to be autistic, only it's so much more complex than that. If scents in this example equate to tone, you also have body language, pacing of speech, context, and a myriad of other "unconscious" and "instinctive" means of communication which you first have to realise exist at all, and then figure out what they mean, and then put them into practice, all the while no one will tell you what these things are, no one CAN tell you how they work as to most people it's instinctive, and no one will believe you don't instinctively know these things either, so if you get it wrong people will refuse to believe you didn't mean to be rude, or cruel or arrogant or uncaring.
Then you have the fact that autistic people think differently to neurotypicals (that's you!) so it's not even like our minds are the same and we just need to translate it correctly with the "unconscious" toolsets we have to try so hard to use with conscious effort. We have to translate how we think too, and translate other people's thought processes into something we can understand.
It's exhausting. And it's why, despite the fact I can appear more or less normal and I can get on pretty well these days, I will always struggle, I will often burnout, I will have breakdowns and shutdowns, and I need a lot more time on my own recovering than most "normal" people. It's why I struggle in loud and busy environments, why I go quiet sometimes, and why I sometimes just need to leave an environment despite the fact that everyone else is having such a good time and I'm being "selfish" wanting to leave.