Philo Judaeus De Plantatione 80

[80] As, therefore, some of those who have dug wells have often done so without finding water; so likewise those who advance far in knowledge, and who have made great progress in it, are still often unable to attain to the end which they desire. At all events, they say that men of extensive learning often find fault with their terrible ignorance, for they only just know how far they are removed from the truth. And there is a story that some man of old time, when he was admired for his wisdom, said, that it was a fine thing that he should be admired, who only just knew that he knows nothing.