not for nothing

Phrase

For an extremely good reason. / Used to soften the impact of what is said next, implying that it is important. / Used other than figuratively or idiomatically: see not, for, nothing.

Japanese Meaning

（非常に良い理由で）……する、というのは、単に偶然ではなく、しっかりとした意義や理由があることを示す表現 / （話の前置きとして）続く内容のインパクトを和らげ、その重要性を強調する際に用いられる表現

What is this buttons?

She kept the secret not for nothing; revealing it would have hurt the family.

Google Translation / DeepL Translation

彼女が秘密を守っていたのは、それには十分に正当な理由があり、明かせば家族を傷つけてしまうからだ。

Details

Sense（1）

For an extremely good reason.

Not for nothing is it called the World Wide Wait. Not for nothing has a Dilbert cartoon appeared noting that all the time saved through automation and computers in the last fifty years has been entirely outweighed by people sitting in front of pc's waiting for web pages to load.

Google Translation / DeepL Translation