The truth of suffering is one of the central concepts of Buddhism religion. The Buddha can be looked upon as a physician who diagnoses and prescribes the path leading to the end of suffering.
Buddhism is looked upon by some as a pessimistic religion since it stresses on suffering. What they forget is that that this is a philosophy that also prescribes a way out. My own view is that Buddhism is based on an understanding of human psychology and that it is very realistic and practical.
Buddhism religion - a path leading to insight