Hi Paco,
I was trying to keep my remark simple. Please let me explain a little more of what was in my mind.
I think that if you asked 'the average English speaker' to write down as many rules about the English language as possible, you'd get a very, very short list. On the other hand, if you do the same thing with 'the average English learner', you'll get a much longer list.
I'm an educated English speaker and I am amazed and intrigued by how many 'rules' that I have never even thought about are quoted by NNS. I'm also intrigued by how accurate many of these rules are, perhaps not in every detail, but close enough to allow pretty good English to be produced.
As a considerable generalization, I'd say the native speakers' big advantage is that, by and large, they have an ear and a 'feel' for what is OK and not OK.
NNS people who write to this forum are often interested in naming structures and other features in English, and analysing the language in terms of the rules, and I'd venture to say that most native speakers couldn't do this and wouldn't be interested in doing this. Please understand here that I see that rules serve a very, very useful purpose, and that I mean what I'm saying as complimentary to NNS people.
Would you agree with all this? In my ignorance of the Japanese language and mind, I would tend to assume that all this is equally true for the Japanese language, and any other language.
Best wishes, Clive
paco