In Sanskrit literature, dukkha was often compared to a large halting and screeching potter's wheel that would not produce good pottery.
As the Buddha said in Samyutta Nikaya #35:
What ordinary folk call happiness, the enlightened ones call dukkha.
The Buddha discussed three kinds of dukkha or suffering:
1. The obvious sufferings of: pain, illness, old age, death, bereavement
2. Suffering caused by change: violated expectations and fleeting moments of happiness
3. Subtle form of suffering arising as a reaction to qualities of conditioned things, including the skandhas, the factors constituting the human mind
The Noble Truth, regarding the origin of suffering (Dukkha Samudaya) reads as follows:
"This is the noble truth of the origin of suffering: it is this craving which leads to renewed existence, accompanied by delight and lust, seeking delight here and there, that is, craving for sensual pleasures, craving for existence, craving for extermination."
Khenpo Dudjom Dorjee teaches on the Truth of the Cause of Suffering: