A-and-B can't beat A
The chance of two things both happening is never greater than the chance of either one alone. Add a condition to a claim and you can only shrink its odds, or at best leave them equal. That is arithmetic, not opinion.
News from Now On · Lab Knowledge Byte
The detailed forecast is the less likely one
Adding a vivid "and then" makes a scenario feel more real. Mathematically, each detail can only make it less probable.
The Linda problem
Tversky and Kahneman described "Linda": a philosophy major, outspoken, concerned with social justice. Asked what's likelier — that she's a bank teller, or a bank teller and a feminist — about 85% chose the second. The richer story felt more representative, though it must be less probable.
4% beat 1%
They ran it on real forecasts. Policy experts rated "a Soviet invasion of Poland, and a break in US–Soviet relations" at 4% likely. A separate group rated a US–Soviet break alone at just 1%. The dramatic extra detail raised the estimate — of a strictly rarer event.
Price the load-bearing claim
Distrust the forecast that reads like a screenplay. Each specific trigger, actor, and date is one more "and" the world must satisfy. Strip a scenario to the single claim it rests on, estimate that, and treat every added detail as a discount — never a bonus.