There is an awesome thread here: https://news.ycombinator.com/item?id=29673707
But reading between the lines it's obvious that the major problem in most cases was lack of demand or inability to market the product.
So I'd be interested hear what and how you do early demand validation for your side project or idea, if any?
Share your story.
* Make it open source
* Give it away for free
It's not the golden rule that will work for everything. But that's what I did with Lunar, my app for controlling monitors (https://lunar.fyi) and it helped enormously with adoption and with seeing if a large enough user base could be created.
A lot of users offered to donate, others told me that I was stupid for not asking money for the app, others constantly asked for features on Github which helped me understand how the product could solve the problem better.
In the end, I prepared a large update with most of the features that were requested and made those features paid while keeping the old version free and open source.
99% of the users applauded this decision and were happy to pay (the other 1% sweared angrily through emails, but what can you do..)