There is a plentiful lack of men so endowed, and it is difficult to form a judgment without testing.
 Marcus Tullius Cicero, On Friendship (44 BC). copy citation

add
Author Marcus Tullius Cicero
Source On Friendship
Topic judgment
Date 44 BC
Language English
Reference
Note Translated by E. S. Shuckburgh
Weblink http://www.gutenberg.org/files/2808/2808-h/2808-h.htm

Context

“and while they took pains in procuring the former, they were utterly careless in selecting friends, and possessed no particular marks, so to speak, or tokens by which they might judge of their suitability for friendship. Now the qualities we ought to look out for in making our selection are firmness, stability, constancy. There is a plentiful lack of men so endowed, and it is difficult to form a judgment without testing. Now this testing can only be made during the actual existence of the friendship; for friendship so often precedes the formation of a judgment, and makes a previous test impossible. If we are prudent then, we shall rein in our impulse to affection as we do chariot horses.” source