Why does a more detailed story feel more likely than a simpler one?

Adding a detail that fits the picture makes a guess feel more likely, even though it can only make it rarer.

The conjunction fallacy is judging a combination of two events as more probable than one of those events on its own. A specific story that matches a stereotype feels right, so we rate it higher. But probability does not work that way: 'A and B' is a smaller group than 'A' alone, so it can never be more likely. Every condition you add can only shrink the odds.

You hear a coworker is quiet, neat, and loves spreadsheets. Asked which is more likely - 'she works in finance' or 'she works in finance and does yoga on weekends' - most people pick the second because it paints a fuller picture. But the second is a subset of the first, so it must be less likely, not more.

A longer, more specific story is always less probable than its simpler part, no matter how well the details fit.

Forecasts, news scenarios, and sales pitches add vivid specifics to sound more convincing - but each detail makes the claim less likely to be true, not more.

More details, smaller box. 'A and B' fits inside 'A', so it can never be bigger.

Learn the idea and practice English at the same time.