I experienced working on a really good product but it never took off to production due to many revisions - conflicting ideas between founders and co-product owners has resulted to a lot of rework and too evolving product roadmap.
The failure to find the product-market fit: if for months a company can't determine whom they're selling the product to.
If the retention and activation rates are low and the company is not addressing the problem.
If users show no eagerness to pay and the company isn't trying to tackle it.