What are the four noble truths? Buddhism’s famed four truths are called noble because they liberate us from suffering. They are the Buddha’s basic teaching, encapsulating the entire Buddhist path.
1. Suffering
Life always involves suffering, in obvious and subtle forms. Even when things seem good, we always feel an undercurrent of anxiety and uncertainty inside.
2. The Cause of Suffering
The cause of suffering is craving and fundamental ignorance. We suffer because of our mistaken belief that we are a separate, independent, solid “I.” The painful and futile struggle to maintain this delusion of ego is known as samsara, or cyclic existence.
3. The End of Suffering
The good news is that our obscurations are temporary. They are like passing clouds that obscure the sun of our enlightened nature, which is always present. Therefore, suffering can end because our obscurations can be purified and awakened mind is always available to us.
4. The Path
By living ethically, practicing meditation, and developing wisdom, we can take exactly the same journey to enlightenment and freedom from suffering that the buddhas do. We too can wake up.
This is again paraphrased at the end of the quote: "misfortune in general is the rule."
And pine for what is not:
Our sincerest laughter
With some pain is fraught;
Our sweetest songs are those that tell of saddest thought.
Yet if we could scorn
Hate, and pride, and fear;
If we were things born
Not to shed a tear,
I know not how thy joy we ever should come near.
- Percy Bysshe Shelley (contemporary of Schopenhauer), from "To a Skylark"
Unless suffering is the direct and immediate object of life, our existence must entirely fail of its aim. It is absurd to look upon the enormous amount of pain that abounds everywhere in the world, and originates in needs and necessities inseparable from life itself, as serving no purpose at all and the result of mere chance. Each separate misfortune, as it comes, seems, no doubt, to be something exceptional; but misfortune in general is the rule.[0]
He defines pain as the 'positive' thing in our lives, pleasure being negatively marked by the absence of pain. He remarks that when we are of perfect bodily health, it is the stone in the shoe that makes its presence known, not the 1 000 000 other things that are going well. He goes on to say that if men didn't suffer ('turkeys fly around ready-roasted' -- paraphrase) they would kill themselves out of boredom.
I've found the "Penguin Great Ideas" translations of his work to be brilliant. It must be mentioned that his views on women are unfortunate, and some insight into why they are so warped might be gained by looking into his life.
[0] https://www.atlasofplaces.com/essays/on-the-sufferings-of-th...
edit: this aligns with the Vedantic definition of pleasure, as the cessation of mental agitation, where mental agitation is thought and its further expression as desire.