One important thing to remember is that we are mere creatures, and God owes us nothing, while we owe Him everything. Not only that, but we are sinful creatures, desperately wicked. If not for so many external restraints which God has appointed in the world (laws, governments, police, society, culture, limitations of power), this would be even more manifest. Because we are human, it is especially difficult for us to consider the end of many other humans, but we think too highly of ourselves.
Consider the demons, angelic beings who were originally created good as the others, before they fell. God made no plan of salvation for them, but left them in chains of darkness to await the day of torment. We find this easier to acknowledge and see the justice and righteousness of God in, and how He reveals thereby His just and good holiness and righteousness in not sparing them. Yet with humans, through which He also reveals His infinite grace and mercy in our salvation from sin, we are more troubled (and rightly so), ultimately because those who end in hell are our brethren according to the flesh, and because we are impressed enough with our own unworthiness and sinfulness, and God's divine perfection, that all things must serve His glory, not ours, because He alone is God.
We are the clay, He is the potter, and He must be free to do as He will with the clay. The vessels made for dishonourable use cannot complain against their maker. Neither can the vessels made for honourable use boast as if they formed themselves.
So on the final day, when God reveals His handiwork, and His righteousness is demonstrated in all things, we will be utterly awestruck, even dumbstruck, for all created things will not be able to say a word, except that He alone is the Lord who does as He wills, according to His own divine good beautiful glorious perfections.
