There is no one who cannot teach somebody something, and there is no one so excellent that he cannot be excelled. To know how to make use of everyone is useful knowledge. Wise men appreciate everyone, for they see the good in each and know how hard it is to make anything good. Fools deprecate everyone, not recognizing the good and selecting the bad.
Maxim 195, page 168, The Art of Worldly Wisdom, B.Gracian, Shambhala, London, 1993 (originally written in 1637)