The Buddha does not merely touch the problem of suffering tangentially; he makes it, rather, the very cornerstone of his teaching. He starts the Four Noble Truths that sum up his message with the announcement that life is inseparably tied to something he calls dukkha. The Pali word is often translated as suffering, but it means something deeper than pain and misery. It refers to a basic unsatisfactoriness running through our lives, the lives of all but the enlightened. Sometimes this unsatisfactoriness erupts into the open as sorrow, grief, disappointment, or despair; but usually it hovers at the edge of our awareness as a vague unlocalized sense that things are never quite perfect, never fully adequate to our expectations of what they should be. This fact of dukkha, the Buddha says, is the only real spiritual problem. The other problems—the theological and metaphysical questions that have taunted religious thinkers through the centuries—he gently waves aside as "matters not tending to liberation." What he teaches, he says, is just suffering and the ending of suffering, dukkha and its cessation.
~Bhikkhu Bodhi, in The Noble Eightfold Path