This is by far the most difficult problem in startups: Should you persevere or pivot?

I think Paul Buchheit's advice is probably the best way to decide. He says to (paraphrasing) "find 100 people that love your product".

It's not enough for you, or a tiny number of people to say your thing is good. You need a sizable (but still very small) number of people to love your product.

It's kind of a "wisdom of the crowds" solution. You might be wrong, your friends might be wrong, but if 100 people love your product it's very likely that you're on to something.