Recently during a meditation, I came to a deeper understanding of the answer to this question. On one level. we suffer because when we are born, although our Buddha nature is fully formed, just like a baby is physically fully formed, it is weak and very fragile.
And instead of being nurtured, like a baby with milk, our life experiences during our formative years, which form our ego-mind, overwhelm the peace and happiness that is our true nature and we suffer. We know all to too well the rest of the story - our true Buddha nature gets buried under the detritus of our life experience and our ego-mind rules. Our Buddha nature, our heart, becomes virtually unknown to us. Until …
On a spiritual, philosophical, existential level, we suffer because for a human to become strong he has to go through the fire, his mettle needs to be tested, he has to experience the darkness in order to appreciate the light when he catches a glimpse of it. Without that experience, he would have no basis for perfecting wisdom, which is knowing that feelings and perceptions lack extrinsic existence, they are instead the product of his ego-mind, and that the ego-mind is not his true self.
And he would have no opportunity to make a choice to follow the light. When he catches a glimpse of the light, the truth, his choosing and committing to follow that light gives his effort strength and meaning.
So the reason everyone suffers is because without suffering, there is no growth, there is no strengthening, and there is no seeing the light. Whether it’s individuals or groups, it is our suffering that molds our character and makes us who we are. If everyone had wonderful, blissful, idyllic lives free of suffering, we would be a very sappy, characterless bunch and we would have no backbone.
For example, people often ask (or at least they used to) what gives Jewish people their character. Think of their resilience, their liberal nature; think of all the Jewish doctors, lawyers, and scholars, etc. The answer is that they have been persecuted for millennia. That and their strong belief in God made them the way they were. However, as Jews have assimilated into the larger culture and been accepted, or in the case of Israel have become the culture, some of the more humane characteristics of the Jewish tradition have weakened. We have become more like the surrounding culture. Witness Sheldon Adelson and other Jews who support Trump.
But most people will still ask the question, “Why?“ Why is all this suffering necessary? And why do most people never see the light, never get beyond their suffering, regardless how it develops their character?
The answer is that there is some force in the universe, like the laws of thermodynamics in the monk’s answer to me, that brings these forces into play. It’s like asking why is their illness? Why is there untimely death? The answer is, “It’s just the way it is.”
Not in the sense of the classic Christian response to tragedy, “The Lord works in mysterious ways.” That implies an active God who controls people’s lives, makes decisions, like a puppeteer. My answer rather assumes that there is some unknowable force in the universe that causes things to be the way they are, not in an individual case, but generally.
And it is necessary for growth and thus something to be grateful for. Some say that the soul actually chooses its life setting and the challenges that flow from it in order to grow.
The teaching of the Buddha is that every challenge, all suffering, is an opportunity for growth and knowledge. It’s up to the individual how he or she responds to these forces.