Schopenhauer is hard to beat. I like that in contrast to Leibniz, who genuinely (as far as I remember from my student days) tried to argue that this is the best of all possible worlds (!!!), Arthur S's view was that it is the worst of all possible worlds, and that the will to live and struggle for everything is the structural source of human torment. Therefore, denial of that will (where/if possible) is key.
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.