Meditations, Marcus Aurelius => A lot of wisdom on how to lead and live

On The Shortness of Life, Seneca => An essay about how to handle life and how to see what is really important

On War, Clausewitz => An important essay about strategy and war, politics and management

The Prince, Machiavelli => A little bit cynical but quite realistic about the nature of power in the hands of humans

Thirty-Six Stratagems, multiple authors => A list of strategies that can be used in any situation, whether when winning or losing