I was reading the book 'The Memoirs of Sherlock Holmes' and found this interesting case called - The Yellow Face. This is a good read. Sherlock is asked to help a man who feels that there is a secret between him and his wife. Sherlock suspects that its the lady's first husband who has come to the cottage and blackmailing the lady, along with another lady.
Only when they reach the cottage, Sherlock and the man realize that it is not the first husband but the child who was unwell and has now recovered. So, Sherlock fails to solve the case or to be fair, his assumptions and inferences about the case is false.
After reading this story, I realized that investigation is a key skill in software testing as well. Think about how we listen to the facts, lay our assumptions, build a story, conduct experiments and prove our theories or learn from it. Sometimes we go ahead and without any experiments, conclude that our theory is correct. Just before the story ended, Sherlock tells Watson
'If it should ever strike you that I am getting a little overconfident in my powers, or giving less pains to a case than it deserves, kindly whisper 'Norbury' in my ear, and I shall be infinitely obliged to you.'
Just when I read those words, I felt that it can be turned into a heuristic - "The Yellow Face" heuristic. A heuristic which warns the testers against complacency. Against believing a theory without enough investigation, without enough critical thinking.
Imagine in a project when someone is building assumptions after assumptions, just tell them - Beware of the yellow face heuristic