1/ Startups fail for a whole lot of reasons, and yes there is some nuance to it. But I've consistently seen it boil down to two areas.
2/ First, disclaimer this applies mostly to b2b products especially developer and data products. I know nothing about the consumer space other than I am one.
3/ So the first big reason is you're a product in search of a problem. You built something that is interesting and try to go and find a need for it.
4/ If you can't describe at the most basic level what problem you're solving in 30 seconds, you may be in that category
5/ The other big reason is a bit more complicated, the overarching bucket is you couldn't figure out how to make an grow your business and couldn't get all the non engineering pieces working
6/ The best engineers I've worked with appreciate sales/marketing/BD as much as they do engineering, maybe even more. They've over an past engineering purity and that this stack is "better". PHP still works, Rails still works, your success is not likely dependent on your stack
7/ Rather, product market fit, marketing, sales start with knowing who the buyer is-you need to know who owns the purchasing decision
8/ Once you know your customer you need to basically orient each area of your go to market around how to reach that customer, how to streamline your sales, make the product easier to adopt
9/ There are definitely some exceptions (raise too much, grow to fast, etc.), but if you zoom out it's one of these two.
10/ One small revision... it may also fail because you moved to the yet again shiny new JS library that was released last week that engineers fell in love with but actually makes no material impact for the product you ship