Throughout your journey, from concept to growth, a lot of people will be giving you their advice on what to do, how to do it, will it succeed, will it not, how will people react etc. etc. All of which are purely subjective. Subject to biases, opinions, sometimes even malice and an uncontrollable urning to see you fail.
So the only purely un-bias opinion you can get is from your end user. People who have no stake in your success or failure, and if anything, whose positive opinion will most likely ensure your success.
So identify your target market, get a sample audience together, build a database of possible end users, and survey the hell out of them in order to get the best possible feedback to whatever it is your doing, or will do.