Sherlock Holmes Has Been in Print for 139 Years. The Character Is Still Being Solved.

The question Conan Doyle never quite answered was whether Holmes was a machine running a program called curiosity or a person who had been damaged into performing certainty. Every adaptation since has chosen a position on that axis, and none of them have been entirely right.

The original stories hold together precisely because they are ambiguous on this point. Watson observes; he does not explain. The reader gets Holmes through the effects he produces on other people. The moment any adaptation tries to show the inside of Holmes's head directly, the character loses whatever made him interesting.