the most authentic master I ever encountered
Something in prolonged contact with rouge eventually becomes red, something in prolonged contact with soot eventually becomes black. What I realize as I observe this is the tao of habituation to good and bad.
When you live with good people, what you always hear are good words and what you always see are good actions. Hearing and seeing good words and actions over a long period of time plants good seeds in your mind, so that you spontanteously become accustomed to goodness.
When you live with bad people, what you always hear are bad words and what you always see are bad actions. Hearing and seeing bad words and bad actions over a long period of time plants bad seeds in your mind, so that you naturally become accustomed to badness.
Good and bad people are said to be so by nature, but most become so through habit. Therefore wise people choose their associates carefully.