Whoever told you to not start that thing because it won't make any money was kind of missing the point.
The fact that you're driven by your passion for the idea and not by the money it (might) make is exactly the reason why you should be pursuing it. An idea that's being fuelled by dollar signs is an idea that lacks integrity anyway, and integrity is the secret ingredient of successful anything these days.
If you're being lit up by something other than the notion of getting rich, then I implore you to follow whatever it is that's calling for your attention. Explore it, humour it, allow to emerge whatever it is that wants to. Be curious and let the ideas flow, because you just never know. You've no idea why you're being led down this path of interesting new things, you've no idea yet what chance encounter is leading to another one that hasn't even revealed itself yet. The very fact that you're interested in something for all sorts of reasons other than money means you're being called to something. Don't hinder the magic of it with dull logistics like whether or not it will earn you a living, that kind of stuff shouldn't be anywhere near your radar (for the moment anyway).
Inspiration is a wonderful thing, like being a kid again, looking at the world with excitement at everything new. Let yourself be that kid. Forget about the money, just enjoy yourself - feed your soul.
Start that thing. Explore the possibilities of the idea. You just never know.
If you've got an idea you're ready to explore further, be sure to get my free training that gives you the essentials of turning an idea into a small business - get it for free when you sign up for my newsletter.