One of the great things about learning a language, is that you know when you know a language point. You don't need confirmation from anyone, because you're using it in a conversation (spoken or written) and the person answers, meaning that you accurately conveyed what you wanted to say when you needed to say it.
Conversely, you also know when you don't know a language point well, or when you don't understand it, because whenever you're using the language you're studying, you push this language point aside and say/write something else.
If you keep using what you know, you stay within your own linguistic comfort zone and you stop making progress. It's a normal, human reaction, because it not only feels familiar, but also safe to stay there.
My job as a language teacher, is to recognise when my students have reached the point where they're sticking to their comfort zone and to kindly nudge them out of it, by getting them to practise and consolidate those tricky language points they're not sure about.
And because, to me, language teaching is inherently collaborative, I make it a point to tell my students when they're sticking to their linguistic comfort zone and to explain what we're going to do next to leave it behind.
Learning a language is a process with learning curves and planes, with accelerations and standstills. And it's never straightforward. But with the right mindset, tools, and method, it becomes a glorious adventure, which is both empowering and fun.
Don't hesitate to send me your questions.