How many programmers would have been unsuccessful if Stackoverflow didn't exist?

Well, there wouldn't be that much of the difference because StackOverflow is just the most popular site for asking coding question, if it didn't exist there would a different one just as big, as long as the internet is open there will always be a site like that. A better question: "How many programmers would have been unsuccessful is the internet was not open to the public?"

Forgot all the programmers that came before SO?

I think Github had a much bigger impact. I enjoy seeing how other developers solved a problem I have.

SO pays off in the short term, but in the longer term you are left with nothing but superficial knowledge and badges.

StackOverflow is just the path of least resistance. There was a time when developers would just have framework or language books sitting around for reference.

At least one! Ha ha cries in copy-paste

Way less than if online search engines wouldn't exist

before stackoverflow there was "documentation" and "man pages"; would have worked out alright

All of them.