"Sheol and Abaddon are never satisfied, nor are the eyes of man ever satisfied"
Solomon is saying something incredibly profound and insipidly factual at the same time.
Hell keeps receiving people and never says that it is full and cannot take any more people. And your eyes are never tired of seeing for it is the thing that they do; your soul is never content with what it already has because it can use your eyes to see things that it doesn't have.
This is the Hebrew word Sheol, which has not been translated but rather transliterated. The word has just come into the English language unchanged from the Hebrew. It refers to the place of the dead, the grave, the holding tank for the souls of the departed. At times the word refers simply to the grave and, at other times, it refers to the place that all the souls of the dead went to while awaiting God's judgment. All the dead in the Old Testament when they died went to one of two compartments in this place called Sheol. See Jesus' comments in Luke 16 about the rich man and Lazarus. The two compartments were named Abraham's bosom for the righteous and Hades for the unrighteous. The early church maintained that Jesus – when he died on the cross – went to the upper part of Sheol and preached to those in the upper chamber of His rescue of them, and He preached across the chasm about the doom of the unrighteous angels and men that His work on the cross accomplished. 1 Peter 3:18-20
This is the Hebrew word Abaddon and is again a transliteration rather than a translation. This word means to die, destruction, ruin. It became associated with the place of destruction and ruin after your die. In Revelation 9:11 it is used as the name of the powerful angel who comes up out of the bottomless pit and wreaks havoc on the earth. It is, therefore, thought of as referring to the bottomless pit which seems to be a sub-region of the bad compartment of Sheol.
Solomon is clearly trying to point out two things that never say enough. They are never full; they keep receiving people. Everyone knows that there will never be a time when death and hell are ever full and unable to receive any more today. This is Solomon's point as he gets us to focus on things that are never satisfied.
eyes of man
The word eyeis the Hebrew word ayin, which means source, to behold, and eye. This word is also used in a figurative sense in that it stands for the soul. Technically the eyes don't do anything but transfer light impulses to the brain, but they are extensions of the soul and its windows on the world. John the Apostle says in 1 John 2:15-18 that the sins of the world are the desire of the eyes, lust of the flesh, and the boastful pride of life. It is not that the eyes want anything, but they are directed by the soul of the person.
In this proverb, Solomon is pointing out that no matter what you possess, there is always something more to possess. When you ask the question “What do you want?” there is always an answer. If we are going to be content in our life, we must realize that there will always be another thing to want or desire. But at some point you must enjoy what you have. You need to focus on what God has given you instead of always looking for what you hope He will give you. Your eyes or desires can make you never satisfied, no matter how good things are.