I am an amazing English speaker.
I can work as a software engineer, file a tax return, and ask for directions to the bathroom, all in perfect English. Of course, I don’t expect much respect for speaking English like a native speaker, because… I am a native speaker. My amazing English prowess is about as impressive as getting out of bed this morning.
Another dubious skill of mine is my supremely excellent speed of forgetting. Thankfully, I am good at taking notes.
The most impressive thing I have forgotten is my native language. I was studying at an intensive Mandarin school for a little while. During the course, I spoke almost only Mandarin. One evening, I was speaking to an American for a change and deployed the aforementioned amazing English skills.
What came out of my mouth was a hesitant sort of beginner’s English. I knew what I wanted to say, but the words weren’t quite coming to mind. I had managed the impossible and forgotten my native tongue.
I have no good advice for learning anything, but I can say with great confidence that I have discovered the most effective way to forget everything: Stop practising.