For example, I just learned about f strings, because why would I need to ever look up if there is a replacement for .format()?
And the LRU cache. I've been hand rolling that for years, but I never thought to see if they had added it to the standard library, because why would I look?
I hand rolled stuff in itertools/functools for years before discovering them.... collections Counter, etc.
Or how about str.partition instead of try: str.split() ?