These characters combine literally and elegantly: 无 (without) 事 (an issue) 生 (create) 非 (conflict). The meaning is transparent—to create conflict when there isn't an issue to begin with.
The idiom 无事生非 is deeply rooted in the Chinese cultural emphasis on social harmony (和, hé). Traditional Chinese values prize stability, peace, and smooth interpersonal relationships. Acting in a way that disrupts this harmony without cause is seen as immature, foolish, and highly undesirable.
This idiom is extremely common in everyday life and carries a strong negative connotation. It's a form of accusation or a sharp piece of advice.