In the mid-1980's researchers at Cleveland State University made a startling discovery.

They conducted an experiment by creating two fictitious job candidates David and John. The candidates had identical resumes and letters of reference. The only difference was that John's letter included the sentence "Sometimes, John can be difficult to get along with". They showed the resumes to a number of personnel directors. Which candidate did the personnel directors overwhelmingly prefer? Difficult to get along with, John.

The researchers concluded the criticism of John made praise of John more believable. Admitting John's wart actually helped sell John. Admitting flaws gives you more credibility. A key to selling.