It is one thing to do..., another to do...

是一回事，…又是另一回事。

youdao

This highly analogous recent legal precedent will make it hard for Google to deny the FTC has Section 5 authority over Google or to claim that it is not deceptive for Google to represent one thing to the public and do another.

FORBES: Do No Evil? Google's Deceptive Practices Harm Consumers

Yet it is one thing to recognise a problem, and quite another to do something about it.

ECONOMIST: France��s economy