Who said "It is not possible that I should be mistaken."?

This quote is attributed to Sherlock Holmes.

It is not possible that I should be mistaken. - Sherlock Holmes

"It is not possible that I should be mistaken."

Sherlock Holmes

Character in The Hound of the Baskervilles

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"The world is full of obvious things which nobody by any chance ever observes."

"The moor is a dangerous place, Watson."

"I cannot but think that you are justified in your caution."

"One should always look for a possible alternative."