The note about the GIL is buried pretty deep in the threading documentation, and this makes it hard for first time users to discover why their attempts at using threading to parallelizing their application did not work.

This used to be the case in the old Python 2 documentation, but https://github.com/python/cpython/commit/d6d17c58af8002000ecd1326c7accafb5af8a9db moved it, and no corresponding discussion exists. I think the GIL is a pretty important thing to mention, especially for people used to other programming languages. I believe the change had a negative effect and should be reverted.