Idiom/成語 for "Worrying Doesn't Change the Outcome"
杞人憂天:

There was a man in Qi always worrying about the sky might fall. People use the term 杞人憂天 to describe someone worry too much, even about the most unlikely events.

Example:

Worry about car accident is one thing, worry about alien invasion or zombie apocalypse is really 杞人憂天