My wife and I have a joke about using a tree as a landmark. In most places, trees are too common for that to work. You need something uncommon, or less common, to ensure you keep following the right path.
In language study, of course you start by learning the most common words and sayings. That’s good. Sooner or later you’ve learned the most common 1000 or 2000 words. You can express a lot with these words, and you can understand a lot of what people around you are saying. You can get around, meet basic needs, and carry on basic conversations.
In my pride about learning so many of the most common words in Chinese, I didn’t expect I’d still end up lost, conversationally speaking, so often. Then I realized: the most common words in my mother tongue (English) are not always the words that carry the most significant meaning in conversation. The common words usually provide context for the most important words. (For example, in a paragraph about the Civil War, the majority of statements could be comprised of very common words. But the words that tell you that the paragraph is about the Civil War might be much less common.)
So we often find ourselves nodding while our friend talks away, hoping that although we don’t recognize several important words, the common words we do recognize will give us enough context to give us a general idea of what he’s saying.
The trees go flashing by, and we frantically hope we don’t miss an important landmark. Frantically hope we didn’t just miss a turn in the conversation, agree to something outrageous (or unbiblical), unknowingly commit ourselves to something we’d rather not have, or miss a cue to affirm our interest.