Rigid, overly formal or literal; square and inflexible in thinking or behaviour — a four-character idiom.
彼は規則に厳しく、四角四面なところがある。
He is strict about rules and can be rather rigid.
創造的な仕事には四角四面のやり方は向かないことが多い。
A rigid, by-the-book approach often doesn't suit creative work.
四角四面に考えず、もっと柔軟な発想を持とう。
Don't think so squarely — try to be more flexible in your thinking.