The opposite of Hubris is Sophrosyne (σωφροσύνη). It is considered an important quality to have and is expressed in opposition to the concept of hubris. The meaning of the concept Sophrosyne is, "an ideal of excellence of character and soundness of mind." No language has an equal word to Sophrosyne.
When one has Sophrosyne, it leads to other qualities of humble importance. Qualities are such: temperance, moderation, prudence, purity, and self-control.
The word Sophrosyne was used in Plato's writing and my have been influenced by Heraclitus. His fragment 112 states, "Sophrosyne is the greatest virtue, and wisdom is speaking and acting the trust, paying heed to the nature of things."
Sophrosyne is also a personified daemon. She was released from Pandora's jar and left the cosmos on her way to Olympus.