When do you know that your idea will never work??

You know your idea will never work when you solve your own problem then stop using your own solution.

I'm thinking of shutting down a Shopify project not because there's not necessarily a market, but because I don't have the time to dedicate to doing it properly. By shutting it down, it'll free some mental bandwidth.
I've learned a fair bit from the project, so while it cost me around $1200 (+my time) over 6 months, I see it as an educational cost.

Here's a quote which I find very useful:

"On its path to success, a startup must solve two key problems. The first is to develop and distribute a product that creates significant new value for its users. The second is to capture a meaningful proportion of that value."

The first question is all around 'jobs-to-be-done' - i.e. does a genuine problem exist, for whom, and how are they solving it at the moment?

The second question is a commercial question. Presuming you are creating value for users (i.e. the first question is positive), will people pay directly or indirectly for it?

I've been working on an idea for 18 months and still working on the first question. I'm not convinced I've done it the right way, and it seems much healthier to take multiple, smaller bets rather than put all your energy and focus into one unproven idea.

when heroku pulled the plug.

Honestly, I consider this to be a really hard topic, because it's not easy to find out what exactly is the problem.

1. Are you marketing towards the right target group? In fact, what is your target group?
2. Do you have a good positioning or does your landing page not connect to your target audience.
3. Are you building something nobody wants?

There are many things which you could probably do wrong and I think you have to find out what exactly is the problem. I think the best approach is to really measure and observe your progress. Especially interview or write emails to potential customers and ask them why they like/dislike your product, how they got aware of you, what they would improve...

We are also very new in this topic and actually struggling to make people to get aware of our project (https://turtle.community). I have the impression that marketing is really much effort. Many people say that you have to try lots of different approaches and that marketing is not a one-time effort.

It's very, very hard to know. In fact, many, many failed Dotcom startups now have analogous companies who have recently taken the same idea and made it into a success.

Webvan was a horrible failure. How could you deliver groceries to people over the internet profitably??? Well, it turns out the idea was just 15 years before its time. Instacart made a great business doing exactly that.

I can never say for sure but I would have severe doubts if I have to offer it for free to get people to use it. Another one would be if I am having trouble explaining how it works or why someone would buy it.

What are the signals to identify your idea will never work ??
Never say never!