It is a capital mistake to theorise before one has data

A foggy gaslit London backdrop, a scatter of clue dots, and a magnifying glass hovering over the lot. Above it, Holmes's own line: it is a capital mistake to theorise before one has data.

Straight out of Conan Doyle, public domain and still the best telling-off ever given to someone who's made their mind up too fast. Good for the office overthinker, the amateur sleuth, or anyone who insists on seeing the evidence first.

Part of a matching set of mugs sharing the same foggy London look, so it holds its own or lines up with the rest of the collection on the shelf.