Isn’t it a lot faster to study common vocabulary and grammar?

It really isn’t. It may be the most practical thing to do if you’re just going to travel to the country once and want to learn to order a coffee and say “thank you”, but if you want to really be able to understand the language being spoken to you and be able to hold conversations, there are two main reasons why memorizing vocabulary doesn’t work:\n\nYou forget it as fast as you learn it. When learning words as individual items out of context, you are building very flimsy brain connections. This is what happens when you cram for an exam and two weeks later you have forgotten everything you learned. When language learners say that they have forgotten most words they learned after a few months of not using the language, it’s because they didn’t really acquire those words. They just studied them. This strategy is unsustainable after a certain amount of words, since you’ll be forgetting words as fast as you are memorizing new ones.\nYou aren’t acquiring it. When you use conscious studying, you may have connected that word to an equivalent word in your language or to a picture. However, this kind of conscious learning still requires you to consciously think about the word and translate it in your head everytime you hear it or you want to say it. If you have to do this for most of your vocabulary, it will be impossible to follow any kind of moderately-paced conversation, or to be able to spontaneously produce your own sentences without the listener getting bored of waiting and leaving. In addition, because you haven’t encountered the word in a large number of sentences that you could understand, you won’t know how to use it correctly in a sentence, in which contexts it can be used, or its nuances.