The First Noble Truth

Suffering (Dukkha)

Suffering comes in many forms. Three obvious kinds of suffering correspond to the first three sights the Buddha saw on his first journey outside his palace: old age, sickness and death.
But according to the Buddha, the problem of suffering goes much deeper. Life is not ideal: it frequently fails to live up to our expectations.

Human beings are subject to desires and cravings, but even when we are able to satisfy these desires, the satisfaction is only temporary. Pleasure does not last; or if it does, it becomes monotonous.
Even when we are not suffering from outward causes like illness or bereavement, we are unfulfilled, unsatisfied. This is the truth of suffering.
Some people who encounter this teaching may find it pessimistic. Buddhists find it neither optimistic nor pessimistic, but realistic. Fortunately the Buddha's teachings do not end with suffering; rather, they go on to tell us what we can do about it and how to end it.
http://www.bbc.co.uk/religion/religions/buddhism/beliefs/fournobletruths_1.shtml