This is something that people overlook quite often. It is very important to have a well-documented, up-to-date, and capable standard library packaged with your language. It just creates a smoother experience altogether.

Besides that, it also sets the standard for the 'right' way of designing your interfaces and whatnot. In Go, the third-party libraries are often compatible with the standard library methods and interfaces, which is just fantastic in both mobility between libraries, and having consistency with different projects.