Sometimes I think about how many little things we probably do every day that would totally mess up the reasoning of a Sherlock-Holmes-style detective.
Like the other day we went to the cinema and I was wearing a shirt with no pockets so I put the ticket in my trouser pocket. The next day I was wearing the same trousers and I put my hand in my pocket and found the ticket there.
Now, I have a certain selection of things I always have in my trouser pockets and I don’t really like having anything else in there because it confuses my hands when I want to get something, so I took the ticket out. And I wasn’t near a rubbish bin, but I was wearing a shirt with a breast pocket. So I put the ticket in the shirt pocket.
And I thought: if I get interestingly murdered, the Sherlock-Holmes-style detective is going to deduce that I’m wearing the same shirt that I wore yesterday. Because it’s got a cinema ticket in the pocket with yesterday’s date on, and why on earth would anyone put a cinema ticket in the pocket of a shirt unless they were wearing the shirt when they went to the cinema?
Which is a bit of reasoning we would all find totally convincing if it came from a Sherlock-Holmes-style detective. But it would be wrong. Because actually there are so many other explanations for things once you take account of the fact that people are often slightly eccentric in completely trivial and unguessable ways.
“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!”
—Terry Pratchett, Feet of Clay