Robin, I understand what you mean. Training makes one's language skills automatical, and learning tables of grammar is useless without much application.
Probably you forgot how you started learning English. But can you speak, read and write in Russian, if you don't know what object and dative case are, it's endings, what prepositions are used with it? I mean if you study the language as an adult. And if you know nothing about declension at all (if you are an English native speaker, for example)?
I don't believe that an adult can study a foreign language without learning grammar.