Is tech-stack correlated with success?

Yes, although maybe differently than you think. I've seen products die because they started on a novel tech stack that the creators were lacking proficiency in and that they were not able to get cheap expert help for.

Haven't heard of a product failing only because they were using PHP, Rails or Django – no.

Unless you're working on something where technology and speed is a core promise — then no. Tech stack won't matter.

From my experience, there is a correlation between the tech-stack and the success of the company, at least in the early stages: using technology you know -> faster results. And since speed of execution is one of the most critical, if not the most critical aspect of launching a software product, it will lead to a more successful company, at least in the early days.

If you're a C++ guru and can write webservers in C++, go for it. Learning Golang or Elixir will most likely slow you down in your dev process and result in product that adapts to new learning slower.

There definitely are instances where it matters, and that's probably below 1%. Build with what you are most comfortable with.

I believe no. But the correct stack can speed up your development and lower the expenses.