Related:

• Opportunity may knock only once, but temptation leans on the doorbell.
• Knock, Knock. Who's there? Opportunity. Don't be silly - opportunity doesn't knock twice!
• Opportunity knocks but temptation rings the bell.
• Knock, Knock. Who's there? Opportunity. Don't be silly - opportunity doesn't knock twice!
  -- Norman Dale...
• Opportunity... often comes disguised in the form of misfortune, or temporary defeat.
  -- Napoleon Hill...
• The trouble with opportunity is that it always comes disguised as hard work.
  -- Herbert V. Prochnow...
• ASPERSE, v.t. Maliciously to ascribe to another vicious actions which one has not had the temptation and opportunity to commit.
  -- Ambrose Bierce, "The Devil's Dictionary...
• If opportunity doesn't knock, build a door. -- Milton Berle, comedia