This is what I was told by startup mentors and have come to appreciate as well in my experience.

I would also add that while there is some small risk of someone least copying your idea, it's not necessarily a bad thing. If someone else is doing it, it validates that there is a market. You can also expect that if your idea becomes successful it will be copied at some point.

There's actually much more risk in not learning the practicality of it and refining it by talking to as many people as possible than there is from it being copied.