You need to make sure people will buy your app before building it, because you liking an idea doesn’t mean lots of people will like an idea. Even if a few others have told you the idea is brilliant, that doesn’t mean it will actually sell well.
Take, for instance, celery. Most people don’t like celery, but celery-lovers do exist. If your app idea is celery, that’s fine. Not everyone is making an app for the masses. Some apps, like bird song libraries and Spanish-Portuguese dictionaries, will just not be needed by everyone. What isn’t fine is assuming your app is cake, when your app ...