About this quote

Good reasoning begins by getting rid of what can't be true so you can face what actually remains. Check the facts that contradict each possibility and put those options aside. Have you examined every assumption and knocked down the impossible explanations? When only an unlikely answer fits the evidence, accept it as your working hypothesis and test it directly.

When to use it

• At the security review after a data breach, the lead engineer said, "We've ruled out internal error and software bugs, so the thing left has to be an external exploit."
• In a forensic chemistry lab, the instructor told us, "If contamination and instrument error are impossible here, then the odd result is the real effect and we should follow it up."
• After a dozen negative scans, the clinic team agreed, "We've excluded the common illnesses; the remaining rare condition must be treated as the likely cause and checked."
• When the family couldn't find a hidden heirloom, my brother said, "We checked the usual hiding spots—if none are there, the only place left, however strange, must be where someone put it."