I was taught grammar when I was at school as part of English Language classes. However, in everyday life, as I grew up, I paid very little attention to grammar when I spoke. That's because it was not necessary. Natives will instinctively know what other natives are all talking about, even with bad grammar. It does not mean that when necessary, in a formal situation we will not change and speak with near perfect grammar, it just means that we are more relaxed with grammar in everyday speech.