Diogenes

As a matter of self-preservation, a man needs good friends or ardent enemies, for the former instruct him and the latter take him to task.
As a matter of self-preservation, a man needs good friends or ardent enemies, for the former instruct him and the latter take him to task.
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These are some quotes by Greek author Diogenes Philosopher, who lived between 412 BC and 323 BC.