Two psychologists, Peter Ditto and David Lopez, told subjects that they were being tested for a dangerous enzyme deficiency. Subjects placed a drop of saliva on a test strip and waited to see if it turned green. Some subjects were told that the strip would turn green if they had the deficiency, and others were told that the strip would turn green if they did not. In fact, the strip was just an ordinary piece of paper that never changed color.

So how long did subjects stare at the strip before accepting its conclusion? Those who were hoping to see the strip turn green waited a lot longer than those who were hoping not to. Good news may travel slowly, but people are willing to wait for it to arrive.