Progress in language learning is like an upside-down hockey stick. During an initial period of study you actually progress quite noticeably. From not being able to say anything, you all of a sudden can actually say something in the new language. You can even understand or read something in the new language. Wow!
That is the first steep growth period. That is the blade of the upside-down hockey stick. Most learning material is directed towards this first stage. Teach Yourself Dutch! (Korean, Swahili, Greek, etc.) You cover the usual subjects like the train station, the bank, the post office etc. However, you still cannot carry on a conversation. You still cannot function at the train station, bank or post office. In a way you have an ornament and not a useful tool.
It is the next long stage of language learning, the shaft of the hockey stick, that is the most difficult. There are so many words to learn. Many important words and phrases do not appear often enough to be easy to learn. Instead they are just easy to forget. It is during this period that you need interesting content to keep you going. You need lots of exposure to the language, listening and reading. You need a systematic way of accumulating and retaining words and phrases. You need practice in writing and speaking. This is a long road.
In a way The Linguist system was developed to help people make meaningful and constant progress on this long road.