Discipline

No horse ever gets anywhere until he is harnessed. No steam or gas ever drives anything until it is confined. No Niagara is ever turned into light and power until it is tunneled. No life ever grows great until it is focused, dedicated, disciplined.
— Harry Emerson Fosdick

I've never known a man worth his salt who in the long run, deep down in his heart, didn't appreciate the grind, the discipline. … I firmly believe that any man's finest hour—this greatest fulfillment to all he holds dear—is that moment when he has worked his heart out in a good cause and lies exhausted on the field of battle victorious.
— Vince Lombardi

Life is tons of discipline.
— Robert Frost

(Quoted in John Maxwell's Leadership Wired Newsletter)