There was a girl in my year 10 English class who read the first paragraph of a book*, proclaimed 'I don't get iiiiit and then refused to read for the rest of the week. Later on that year she asked aloud how to spell the word 'toast'. And she had no learning disability that I know of; she'd just managed to get to the age of 15-ish without ever reading a fucking book.
When I was a student, I worked in a Pharmacy. I repeatedly had customers have me search the whole shop, adamant that their prescription should be around - I'd check the sytem, and they'd tell me that whichever prescription we'd last produced hadn't yet been picked up - and then they'd realise that no, actually they did pick it up after all. Or alternatively, they'd watch me scour the shop and then mention that the item they're looking for is usually delivered, a detail which means that it will purposefully be separated out from all the usual prescriptions, meaning that I could have found it straight away if they'd just thought for one second about what information might be useful.
Plus, whilst I was working there, a patient asked me if she still needed to take the pill if she'd had sex on the first day of her period. I was astounded.
Stupid people are everywhere. They crawl up from the cracks in the pavement in order to fuck with non-stupid people.
*Very slowly. It was Of Mice and Men by Steinbeck if anyone's bothered.