The answer is not “never”. That’s the newbie die-hard answer.
One answer is when you haven’t even begun to fight yet (eg not raised the first round) AND you are still hearing what you were hearing a year ago.
That means you aren’t making progress.
Unfundable is sometimes the provenance behind awesome startups. But it usually is not. And if you have labored away for a year, well.
So my advice is: restart or go get the resume somewhere to become fundable.
Don’t give up. Go forward.