In the traditional biography of the Buddha, four sights first revealed human suffering to Siddhartha Gautama.
The four sights are an old person, a sick person, a dead person, and an ascetic. Buddhist tradition says Siddhartha encountered them when he ventured beyond the protected palace environment arranged by his father. The experiences exposed him to aging, illness, death, and the possibility of spiritual liberation.
The story explains why Siddhartha began questioning luxurious household life and eventually left the palace. Different retellings vary in narrative detail, but the four-part structure is consistent across major Buddhist traditions. The ascetic is not itself a form of suffering; it represents a possible response to the other three sights.