That was a good reply which Diogenes made to a man who asked him for letters of recommendation:
"That you are a man, he will know when he sees you;--whether a good or bad one, he will know if he has any skill in discerning the good or bad. But if he has none, he will never know, though I write him a thousand times."
It is as though a piece of silver money desired to be recommended to some one to be tested. If the man be a good judge of silver, he will know: the coin will tell its own tale.