笑う門には福来る (わらうかどにはふくきたる): laugh and grow fat; good fortune and happiness will come to the home of those who smile

笑う門には福来るわらうかどにはふくきたる

laugh and grow fat; good fortune and happiness will come to the home of those who smile

Fortune comes to a house where people laugh. Said to lift a mood rather than to explain anything.