Practically speaking, what's the difference between your program giving incorrect results because you wrote a bug in your code, and it doing to because of a bug

Practically speaking, what's the difference between your program giving incorrect results because you wrote a bug in your code, and it doing to because of a bug in a third-party library, or in the language itself? I mean, the end result is the same. In all cases it's debuggable - the language itself is also just a large piece of software. And if these things are practically the same, and 90% of your bugs come from your own code, and 90% of the remaining ones from third-party libraries, how much do the last 1% bugs really matter?