The unhappy are egoistic, spiteful, unjust, cruel, and less capable of understanding each other than fools. Unhappiness does not bring people together but draws them apart, and even where one would fancy people should be united by the similarity of their sorrow, far more injustice and cruelty is generated than in comparatively placid surroundings.

The unhappy person resents it when you try to cheer him up, because that means he has to stop dwelling on himself and start paying attention to the universe. Unhappiness is the ultimate form of self-indulgence. When you're unhappy, you get to pay a lot of attention to yourself. You get to take yourself oh so very seriously.

A child gets sick with a chronic disease of unhappiness not from unhappy circumstances but from unhappy people around him. Unhappy people cannot raise happy children; it’s impossible.

Is it not enough that we cannot make one another happy, must we also rob one another of the pleasures that any heart may permit itself now and then? And name me a person who in a bad mood will be decent enough to hide it, to bear it alone, without destroying the joy around him. Is it not rather an inner dissatisfaction with our own unworthiness, a dislike of ourselves that is always associated with envy aggravated by foolish conceit? We see people happy and not made happy by us, and that is unbearable.

Consult your resentment. It’s a revelatory emotion, for all its pathology. It’s part of an evil triad: arrogance, deceit, and resentment. Nothing causes more harm than this underworld Trinity.

You’re resentful of whomever you think is responsible for your pain, or your lack of success, or your inability to choose.

She must be unhappy too. Unhappy people are sensitive to the unhappiness of others.

When in the course of human events somebody does something that puts somebody else to the trouble of adjusting the numb routine of his life, the adjustee is resentful. The richer he is and the more satisfactory he considers his life, the more resentful he is at any change, however minute. And of all the changes which offend people, changes which require them to think are most disliked.

Treat unhappiness as a defect and fewer would embrace it

We relive our worst moments over and over and over instead of letting them go, we pick at the emotional scabs and refuse to let the healing happen and the pain subside. We won’t rest until we’ve made sure someone else feels as badly as they’ve just made us feel. If I have to suffer my entire life I will make sure you see how you’ve wronged me! We cling to the resentments that take up our brain space, waste our time, spin us out, keep us angry and depressed and very often make us physically sick and sometimes even kill us because . . . um, why?

There are reasons we become ill or dispirited. It's what Oriwia was referring to. There's always a cause. Sometimes we bring sickness or punishment upon ourselves through carelessness, distraction, transgression, or failing to dedicate the day or the task. Weak moments may invite wrong forces.
Sometimes sickness is caused by a vengeful person such as Oriwia describes. I have seen those affected by the spite of others become ill, go mad, become lame, turn black, drop dead, die slowly. I have seen their children born with ailments and deformities. (Chapter 25 p198)

The happiness which is lacking makes one think even the happiness one has unbearable.

Our possibilities of happiness are already restricted by our constitution. Unhappiness is much less difficult to experience. We are threatened with suffering from three directions: from our own body, which is doomed to decay and dissolution and which cannot even do without pain and anxiety as warning signals; from the external world, which may rage against us with overwhelming and merciless forces of destruction; and finally from our relations to other men. The suffering which comes from this last source is perhaps more painful to us than any other.

The happier people can be, the unhappier they are.