Letters 9.10

For what purpose, then, do I make a man my friend? In order to have someone for whom I may die, whom I may follow into exile, against whose death I may stake my own life, and pay the pledge, too. The friendship which you portray is a bargain and not a friendship; it regards convenience only, and looks to the results.

Seneca, Letters to Lucilius 9.10, translated by Richard Mott Gummere