Loneliness is an unpleasant emotional response to perceived isolation. Loneliness is also described as social pain—a psychological mechanism which motivates individuals to seek social connections. It is often associated with an unwanted lack of connection and intimacy. Loneliness overlaps and yet is distinct from solitude. Solitude is simply the state of being apart from others; not everyone who experiences solitude feels lonely. As a subjective emotion, loneliness can be felt even when surrounded by other people; one who feels lonely, is lonely. The causes of loneliness are varied. They include social, mental, emotional, and environmental factors.