Cynics are right nine times out of ten; what undoes them is their belief that they are right ten times out of ten.

Related:

• The cynics are right nine times out of ten. -- H. L.
  Mencken (1880...
• Nine times out of ten the statisticians are
  wrong...
• I believe in instinct, not in reason. When reason is right,
  nine times out of ten it is impotent, and when it prevails...
• If someone gives you so-called good advice, do the opposite;
  you can be sure it will be the right thing nine out...
• If people see that you mean them no harm, they'll never hurt you,
  nine times out of ten...
• In a three-storey building served by one elevator, nine times out of ten the elevator will be on a floor where you are not.
  Dedera's...
• Nine times out of ten the man who listens to reason
  is thinking of some way to refute it...
• When I was young I observed that nine out of every ten things I did were failures,
  so I did ten times more work. -- George Bernard...