I find it interesting how often I observe someone give a disclaimer about being bad at English, followed up with the clearest explanation / documentation / answer I've seen in a good month or so.
Possibly you have to be really good at a language to realise how "bad" you are. If you're poor at using a language you can't see your mistakes. As you become significantly better you can appreciate nuance, and such, and again feel inferior.
Too good for someone to realize you are a non-native speaker, and not good enough to not occasionally make obvious mistakes without realizing it.