The Dubno Magid zt”l (Sefer Ohel Yaakov) explains this concept with a parable of a businessman who opened a huge store that sold all kinds of merchandise. The government thought that if someone could open such a big store, he must be wealthy, so they ordered him to pay a large amount in taxes. The storeowner, however, claimed that the merchandise was not his. He had purchased it all on credit. They retorted, “That is proof that you are rich. No one would give so much credit to anyone if he wasn’t very wealthy.”
So too, Pharaoh told Yosef that he had heard that he was a wise man who knew how to interpret dreams. Yosef replied that the wisdom wasn’t his. Rather, the interpretation was given to him by Hashem. Pharaoh then said, “That is proof that you are very wise. Hashem would never give this knowledge ‘on credit’ to someone who wasn’t exceptionally wise and understanding.”
