Fun in language learning:
I wrote "gnu-radio has a steep learning curve" on a mailing list.
A native English speaker commented "[..] steep learning curve would actually mean that you understand a topic quickly". Then I realized: I had never actually thought about the phrase, I had merely heard others using it, inferred a meaning, and then started to use it.
https://en.wikipedia.org/wiki/Learning_curve#In_culture
The thread is here: https://lists.tlug.jp/ML/2601/msg00001.html