Related:

• A sharp tongue is the only edged tool that grows keener with constant use.
  Washington Irving ['The Sketch Book', 1820]...
• The only constant is change.
• This instrument [T.V.] can teach, inform, and even enlighten.
  But only as far as humans are willing to use it to those ends. -- Edward R. Murrow...
• A sharp tongue and a dull mind are often found in the same head.
• Themistocles said that he certainly could not make use of any stringed instrume
  could only, were a small and obscure city put into his hands, make it great and glorious....
• Rule of Open-Source Programming #48: The number of items on a project's to-do list always grows or remains constant.
• The only constant since the beginning of time is change.
• Knowledge is the only instrument of production that is not subject to diminishing returns.
  -- J.M. CLARKE...
• he privileged being which we call human is distinguished from other animals only by certain double-edged manifestations which in charity we can only call "inhuman.
  -- Raphael Aloysius Lafferty...