A test with just three questions is enough to expose how often people rely on their first instinct. The Cognitive Reflection Test, or CRT, is widely described as the world’s shortest intelligence test, yet most people who take it do not get through it successfully.

The test was developed in 2005 by MIT professor Shane Frederick as part of a research project involving 3,000 participants. Among them were students from top US universities such as Harvard and Yale, but many still failed to answer all the questions correctly. The result has made CRT a well-known example of the gap between intuition and careful reasoning.