I'm always on time (except for one misunderstanding about where we were meeting) and I'm really used to everyone else turning up 10mins and more late, in fact, I can't recall many friends being there when they said they would. I don't stress about others being late, unless we're going to something that's starting at a certain time, e.g. a movie. I would give them a half hour, maybe more. When they eventually turned up, I wouldn't let them know that I was annoyed, even if I was a bit. Each time, except one, the person has eventually turned up and has seldom ever appeared sorry or attempted to provide a reason for being late. Once, when I was about 11, they were more than an hour late and never even apologised. I felt like they were treating me like a fool, when I was just a good friend. My executive function isn't great and I've real problems shifting attention, but I watch the clock all the time and, if I have to be somewhere at a certain time, I'll make sure of it, dropping everything else in the process. I'll never forgot to meet the person, as that will have been forefront in my mind all day and any necessary preparations , e.g. packing my bag, will already have been made, long before it was time to leave the house. I've such a disorganised brain, with too many thoughts going on, that I need organisation in my life, to keep the stress down.
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"We act as though comfort and luxury were the chief requirements of life, when all we need to make us really happy is something to be enthusiatic about." Charles Kingsley