Cassius Longinus’s “Cui bono?” is the question to ask whenever you are looking to explain head-scratching decisions you don’t understand or why people act in a certain way. It’s a useful tool for reading the news or helping to arbitrate at work or at home.

Here is an extract from a book about Cicero’s advice on oratory:

“Cicero earlier in the speech had invoked the famous legal maxim of Cassius Longinus, Cui bono (“To whose advantage?” or “Who stood to gain?”), a question invoked still today in court when attempting to establish the probability of motive.”

Here’s the context for what Cicero said in his address to a jury:

“Up to this point, gentlemen of the jury, I see that all the evidence points in one direction—that for Milo, it was actually advantageous for Clodius to continue to live, while for Clodius, the death of Milo was the realization of everything that he had so earnestly desired; that Clodius’s hatred toward Milo was extremely bitter, while Milo harbored no hatred at all;” – Cicero

Follow the money and you normally find out who stood to gain.