I'm serious, things are difficult enough as they are.

我是认真的，事情照现在这样已经够困难的了。

《柯林斯英汉双解大词典》

They are not serious enough at that age.

那个年龄的他们不够稳重。

youdao

They are too serious, too academic and not imaginative enough.

他们太一本正经，太学究气，想象力也不够丰富。

youdao

Although they are rare, they are serious enough that each requires an investigation.

BBC: Devon hospitals report serious surgical errors

Clearly there are serious problems, but they hardly look big enough to set off a crisis at the heart of the global financial system.

ECONOMIST: The crisis in the debt markets

Most businesses are reluctant to invest in cyber defenses because they don't consider an attack a serious enough threat.

WSJ: Israel's Businesses Losing the Cyber War