Conjunction fallacy
The mistake of judging a specific combination of events as more likely than one of those events alone. Adding details makes a story feel more believable while making it less likely.
In everyday life
Told about a woman who cares deeply about social justice, many people rate 'bank teller and feminist' as more likely than just 'bank teller,' which is impossible.
Told your new neighbor is quiet and loves books, you think it's more likely he's 'a librarian who writes poetry' than simply 'a librarian.'
Why your mind does this
Simple, clear options are faster to understand and easier to act on, and when time is short that speed matters. Known odds and complete information feel safer because they let us predict what will happen. Preferring the clear option often saves effort that would be wasted on puzzles we can't solve.
Its family, in 30 seconds: Simple & complete
How to spot it
Notice when adding details to a story makes it feel more likely.
How to counter it
Check each added detail and remember that adding an 'and' can never make a story more likely.