What idea did you initially deem brilliant before you knew better?

• "That smart people could predict the overall movement of stock markets."
  —Alan "Ace" Greenberg, former C.E.O. of Bear Stearns
• "Ethanol from corn."
  —Tom Schumacher, president of Disney Theatrical Productions
• "The reply all button."
  —James Hong, co-founder of hotornot.com
• "Spray-on tan."
  —Max Levchin, founder of Slide.com

• "TiVo."
  —Mike Blum, owner of Pipsqueak Films
• "Jackson Pollock."
  —Irwin Jacobs, co-founder and chairman of Qualcomm
• "The BlackBerry."
  —Jeffrey Katzenberg, co-founder of Dreamworks
• "Google. I was factually and materially wrong at every level."
  —Eric Schmidt, C.E.O. of Google