Short answers, pulled from the story.
The word pessimism comes from the Latin term pessimus, meaning the worst. This linguistic root establishes a baseline for understanding the philosophical stance that life and existence hold negative value.
Arthur Schopenhauer argued explicitly that we live in the worst of all possible worlds during 19th-century Germany. He constructed an entire philosophical system in his work The World as Will and Representation where the inner essence of all things is pure striving that is aimless and incessant.
David Benatar argues there is a significant difference between lack and presence of harms when comparing situations to claim non-existence has advantages over existence. His argument states bringing other beings into existence is morally wrong because severe pains can last days months or years while most intense pleasures are short-lived.
One central point of Buddhism originated in ancient India and asserts that life is full of suffering and unsatisfactoriness known as duhka within the Four Noble Truths. These doctrines analyze suffering origin in craving attachment possibility of its cessation and way leading to this cessation through the Noble Eightfold Path.
Richard Dawkins describes vast amount of apparently pointless suffering in animal world as beyond all decent contemplation while Charles Darwin rejected belief in benevolent God partly because of suffering animals who gain no moral improvement from it. Throughout hundreds of millions years of evolutionary history there has been immense amount of suffering including physical pain emotional distress predation parasitism aggression starvation disease.