For a start, Christmas is supposed to be all about family and being around the ones you love. But sometimes, we don't have a family, or we're estranged from them, or said family is so toxic that spending time with them is painful or even dangerous. Or, through choice or circumstance, we might be so far away from our families that we can't be together for Christmas. So the constant reminders of what everyone else seems to have, but you don't, can make this time of year really quite painful.
(Of course, everyone doesn't have a large, loving family - but when that's the image you see over and again, it's easy to think you're the only one whose life is different.)
And that's before you get to the mechanics of why Christmas can be uncomfortable for autistic people - the changes to routine, the sensory overload, and the complicated social manoeuvring. That's a post for later this week.
But please remember, if you're one of these people full of the joys of the season, that it's not a hugely happy time for some of us. Don't mock us if we don't share your good cheer - we feel quite bad enough already without you reminding us that we're Doing Christmas Wrong.
And please remember, if you're one of the many for whom Christmas isn't a great time of year, you're not alone. There are a lot of us in the same situation. Do what you need to keep yourself safe, sane and as happy as possible.