I was once in that situation, and I learned that yes, you do need to validate that others have the same issue and that they're willing to pay for the solution and that there are enough such people to make this a viable business.

The product I created was a tool for a small niche of artists (of which I was a part). It solved a major problem I had, and I knew that others had the same problem. I even ran it by a few other artists and they loved the idea. What I failed to validate was whether they'd pay for the service. As it turns out, most artists in this niche can't afford to pay even $18/month for a service, and they're just as happy using a manual alternative.