Sir Arthur Conan Doyle is a difficult man to understand. He created Sherlock Holmes, one of the most enduring characters in popular fiction, and redefined an entire genre in a way that's still felt over a century later. The mystery genre became a matter of rational inquiry and deductive reasoning. Which is why people are often surprised to discover Doyle's later obsession with the supernatural. Doyle was friends with Houdini, who spent many years debunking fraudulent mediums and mystics. Doyle and Houdini had a falling out when Doyle refused to concede that Houdini did not have supernatural powers, and was merely an illusionist, despite Houdini's explanations.
While the rational Holmes and the mystic Doyle may seem irreconcilable to us, Doyle didn't see it that way. Embedded here is a 1927 film interview with Doyle, where he explains the origins of Holmes and his own interests in spiritualism.