Standalone 'Quite simple'

Hi!

Recently, I encountered a strange construction. Take a look:

"Quite simple, life cannot be the same."

Please notice that nothing precedes 'quite simple', like the usual 'it is' or some similar introduction you would normally expect. I know that 'quite simply' is the default, but is the quoted option (with 'it is' ellipted) also correct? On a side note, Grammarly corrected it to 'simply' the very moment I typed it, but I would still love to see your feedback!