Shabbos 112b:
If Chazal, who are as Malachei Elyon compared to us, made such comparisons between themselves and previous generations, what does that say about us? Someone once interpreted Chazal’s adage as follows: “if the early ones were sons of angels we are sons of men” – if WE view the earlier generations as angels, then we are worthy of being called men. However, “if the early ones are sons of men” – if we do not recognize the greatness of the earlier generations and view them as mere human beings, “then we are like donkeys – we are not even worthy of being called human beings!”