There is nothing more deceptive than an obvious fact.

This line is spoken by Sherlock Holmes in one of Arthur Conan Doyle’s early Holmes stories, reflecting Holmes’s method of reasoning against complacent “common sense.” In the late Victorian context of Doyle’s detective fiction, Holmes repeatedly warns Watson (and the reader) that what appears self-evident can be a trap: witnesses overlook details, investigators accept the first plausible narrative, and “obvious” explanations often rest on unexamined assumptions. The remark encapsulates the stories’ recurring lesson that careful observation and inference—rather than deference to appearances—are required to reach the truth.

The quote argues that the most dangerous errors arise not from obscure mysteries but from what seems plain. An “obvious fact” can deceive because it invites premature closure: once something looks settled, people stop questioning it, fail to test alternatives, and miss contradictions. Holmes’s point is epistemological as much as practical—certainty based on surface appearance is unreliable. The line also functions as a critique of conventional reasoning: the mind prefers neat stories, so it treats the apparent as the real. Doyle uses this idea to dramatize the detective’s discipline of skepticism, attention, and verification.