Dukkha (Pāli; Sanskrit: duḥkha; Tibetan sdug bsngal) is a Buddhist term commonly translated as “suffering”, “anxiety”, “stress”, or “unsatisfactoriness”.[a] The principle of dukkha is one of the most important concepts in the Buddhist tradition. The Buddha is reputed to have said: “I have taught one thing and one thing only, dukkha and the cessation of dukkha.” The classic formulation of these teachings on dukkha is the doctrine of the Four Noble Truths, in which the Truth of Dukkha (Pali: dukkha saccã; Sanskrit: duḥkha-satya) is identified as the first of the four truths.

Dukkha is commonly explained according to three different categories:

The obvious physical and mental suffering associated with birth, growing old, illness and dying.
The anxiety or stress of trying to hold onto things that are constantly changing.
A basic unsatisfactoriness pervading all forms of existence, because all forms of life are changing, impermanent and without any inner core or substance.The Buddhist tradition emphasizes the importance of developing insight into the nature of dukkha, the conditions that cause it, and how it can be overcome. This process is formulated in the teachings on the Four Noble Truths.