Biases in thinking
Dunning-Kruger effect
People with little skill in an area tend to overrate their ability, partly because they lack the knowledge to see their own mistakes.
Judging how good you are at something takes some of the same skill as doing it. Beginners can't see what they're missing, while experts often assume a task is easy for everyone.
In products, it shows up when new users skip onboarding they need, and when experts design for people far less experienced than themselves.
In practice
A new user is confident they've set up their security settings correctly and skips the checklist that would show three gaps.
Common mistake
Using it to dismiss people. The size of the effect is debated, and some researchers argue part of it is a statistical artefact.
Where it comes from
Described by David Dunning and Justin Kruger in 1999, from studies of humour, grammar and logical reasoning.