A four-character idiom meaning plain and robust; describing someone or something sincere, unadorned, and strong in body and spirit.
彼は質実剛健な働きぶりで、周囲から信頼されている。
He works in a solid, unpretentious way and is trusted by those around him.
会社の理念は質実剛健を重んじることだ。
The company's philosophy values being honest and robust.
若いころから質実剛健な生活を心がけてきた。
I have tried to live a simple and robust life since my youth.