Life of everyone naturally contains much suffering. The suffering include birth, ageing, sickness, death, association with the disliked, separation from beloved ones, and not getting what one wants. All sufferings are due to desire and attachment. Suffering stops when desire ceases. The way leading to cessation of suffering is the Noble Eightfold Path.
Wish to never have been born is a desire for non-existence. Wishing to stay young, to have perfect health, to live forever, associate only with the liked, never separate from loved ones, and always get what you want is impossible to be realized. If you accept this reality, see reality as it is instead of wishing it to be what you want to see, you will have no mental suffering. Nobody feels sad when their lottery ticket doesn’t make them rich. That’s because no one really expects to win, although they have the hope. Accept whatever happens, knowing it has to happen due to some reasons, and it is impermanent and just temporary, no amount of emotion can change it, one will stop seeing it as suffering. The problem is not that there are problems; the problem is expecting otherwise and thinking that having problems is a problem.
Buddhists are taught to always contemplate the three marks of existence: suffering, impermanence, and non-self. When one attains the ability to see reality as it is, he is said to have the Right View, which is the first factor of the Noble Eightfold Path. The body is not the real self, and the real self is not inside the body. The body is like an avatar which is remotely controlled by the real self. When the body breaks up, the real self is still around. However, it’s not unchanging. It might take up a new avatar which is another human being, or animal, ghost, deva, or Hell being. If one walks the Noble Eightfold Path successfully and attains Nibbana, he will never be reborn again into the world. No birth means no subsequent suffering; birth is the cause of all suffering, therefore birth is also a suffering. Hence, the best existence is non-existence. To achieve this, one must cease all desires including desires for sensual pleasure, existence, and non-existence. Walk the Noble Eightfold Path but stop thinking about gaining anything any time soon. Not thinking about it does not necessarily mean you won’t get it. A fertilized egg will hatch when the time comes.
A leper has a lot of itches and feels the need to scratch. He is sick. Similarly, feeling the need for sensual pleasure is a sickness. A true man who is 100% healthy will be able to live without desire. No desire naturally means no suffering, here and now. Better still, if there is no more rebirth into this world, then there will be no more suffering forever.