In ancient Rome, when a victorious general paraded through the streets, legend has it that he was somtimes trainled by a servant whose job it was to repeat to him, "Momento Mori: Rembember You Will Die." The reminder of mortality would help the hero keep things in perspective, and perhaps instill some humility.
Sounds like a great add to any leadership training to me. Enjoy the good times, but don't expect that it's your birthright they will last.
Ask Yahoo. Ask MySpace. Ask Netscape. Ask Kodak.
Ask <insert your company here>.