Less-is-better effect
A preference reversal where a smaller or cheaper option is preferred when judged on its own, while the larger or better option wins when the two are compared side by side. Without a comparison, we judge by easy cues like how full or complete something looks.
In everyday life
Seen separately, an overfilled small cup of ice cream seems more generous than a larger amount in a half-empty big cup.
Browsing separate listings, you'd pay more for a 20-piece dish set in perfect shape than for a 40-piece set with a few chipped plates, even though the larger set still has more intact pieces.
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
Ask whether your judgment would change if you saw both options next to each other.
How to counter it
Compare options side by side, using the same measures, before deciding.
Same family: Simple & complete
SourcesHsee (1998)·Wikipedia