Golf=Life..the Spirit of the Game
Golf is played, for the most part, without the supervision of a referee or umpire. The game relies on the integrity of the individual to show consideration for other players and to abide by the Rules. All players should conduct themselves in a disciplined manner, demonstrating courtesy and sportsmanship at all times, irrespective of how competitive they may be. This is the spirit of the game of golf.
-- The Rules of Golf 2008-2009
This is a no-brainer. One should conduct their everyday lives with integrity, even if noone is watching you do it.