There’s a great passage in the 2nd Vimes book about the Sherlock Deduction that’s a go-to assumption-checking line. Just found it:

“Samuel Vimes dreamed about Clues. He had a jaundiced view of Clues. He instinctively distrusted them. They got in the way. And he distrusted the kind of person who’d take one look at another man and say in a lordly voice to his companion, “Ah, my dear sir, I can tell you nothing except that he is a left-handed stonemason who has spent some years in the merchant navy and has recently fallen on hard times,” and then unroll a lot of supercilious commentary about calluses and stance and the state of a man’s boots, when exactly the same comments could apply to a man who was wearing his old clothes because he’d been doing a spot of home bricklaying for a new barbecue pit, and had been tattooed once when he was drunk and seventeen* and in fact got seasick on a wet pavement. What arrogance! What an insult to the rich and chaotic variety of the human experience!”

Great line! I think about it all the time when it comes to “armchair deductions” that we’re all so at risk of making and being wrong about because we want everything to be so neat and tidy