If you have to prove it . . .

In discussing the early stages of the 2008 financial crisis, author William Cohan wrote about an interview that Bear Stearns CEO Alan Schwartz had on March 12.  During the interview, Schwartz said "We put out a statement that our liquidity and balance sheet are strong, and maybe I should expand on that a little."

Cohan reflected on this statement with a reference to Walter Bagehot's comment in 1873:  "Every banker knows that if he has to prove that he is worthy of credit, however good may be his arguements, in fact his credit it gone."

Many people rely on statements of quality in lieu of demonstrated, consistent performance.  

Reference:  William D. Cohan, House of Cards:  A Tale of Hubris and Wretched Excess on Wall Street (New York, Doubleday, 2009), p. 35.