simply; merely; only; used to emphasize that something is nothing more than what is stated.
彼は単に疲れていただけで、気分が悪いわけではない。
He was simply tired; he wasn't feeling ill.
単に数字を比較するだけでは本質は見えない。
Merely comparing numbers doesn't reveal the essence.
単に値段が高いだけで品質が良いとは限らない。
A high price alone doesn't necessarily mean good quality.