When the police interrogate a new suspect, they will often ask a question for which they already know the answer just to test the truthfulness of the suspect. If they can catch someone in a lie, even a very small lie, they will then assume that the suspect is a habitual liar and that anything else they say will be dishonest.

The same principle applies to job interviews and job interviewers know this trick - very well.  If an interviewer has a substantive suspicion that you’re not being honest on some small matter, his confidence in your honesty may vanish in a heartbeat.

Say you’re watching salesman pitching some product on an infomercial. What he’s saying seems to make sense and all of a sudden he says something that you know is obviously not true. You immediately think, “I smell a rat!” and your confidence in his overall honesty instantly evaporates.