How much reviewing can you take?
When it comes to the intensity at which one may make use of a language course, two types of learners can be identified: those who do not move on until they have learned everything in a lesson and those who cannot tolerate reviewing or getting stuck at one single lesson for a long time, and therefore move on even if they have not learned everything.
I personally belong to the second type. I am not really fond of going through the same lesson (or the same movie or novel, for that matter) more than once in order to assure myself that I have mastered the newly introduced words. I do not even appreciate reviewing a textbook as a whole, even though I ended up doing this twice for Mandarin because I realized I could still benefit from studying those two textbooks again.
Now, would it mean that the first learner - the reviewer - learns better and more effectively than the second learner? If the second learner moves on even if they have not yet internalized everything, then how will they be able to keep up with the first learner, who always tries to master each subject they study? The answer is variety of resources. If the learner who does not like reviewing has several textbooks for each language level they wants to study, he can replace the annoying (to their standards) reviews by going through the same subject at another textbook. This can be done by studying both textbooks at once or by picking up the new one having finished with the first one. Either way, the fact that the learner will meet similar words, sentences, grammar explanations and cultural notes in slightly difficult contexts will account for increasing the opportunities for that knowledge to settle in the learner's long-term memory.
As a matter of fact, when a learner studies from two or more textbooks/resources simultaneously they are working towards creating a synergy through the resources, all of them pointing out to a broader sense for the language. This can be done regardless of whether the learner realizes, after the whole process, that they have learned enough to move on or not. When it comes specifically to a perceived lack of sufficient proficiency and a sense of disdain for reviewing, re-reading or repeating, though, it is the approach of using several textbooks of the same level, one right after another that brings the answer to the needs of those who do not like reviewing.
I have tried this approach with Mandarin Chinese. This language is totally different from English and from my native Portuguese. There is almost no common vocabulary, which means each of the 20 or so words introduced at each of my textbook's lessons would be entirely new. With so much new vocabulary, the study would easily get overwhelming and lead to burnout. So, I decided that I would focus on the essential words and ignore the less important ones, according to my level at that moment. I would invariably run into those words at another textbook of the similar level I would take afterwards. As I said above, I did repeat two books that were above the average, but I can asses that I am about to reach an intermediate level in Mandarin by avoiding rote memorization of those 20 or 30 new words I would find at a new daily lesson.
In the case of Norwegian, a much closer language, I found my approach to be even more effective. Just as was the case with Chinese, the mere fact I would be able to finish a 20-lesson book in 20 days worked as a motivation booster. Evaluating your progress in a language may be hard, but evaluating your accomplishments when it comes to finishing textbooks is not. Therefore, I benefited from the large amount of resources I had for Norwegian both at the beginner and at the intermediate stages and after a few months I realized I was seeing the same once obscure words over and over again, and the Norwegian language as a whole started to make sense to me. When I realized that the beginner textbooks were easy, I would skip the first lesson and, in the end, move up to the intermediate ones
It is true that the approach of piling up language resources cannot be used all the time. In the case of less commonly studied languages, such as Georgian, I believe that I will end up reviewing at least some of the lessons that cover important grammar topics. Yet I find it much more challenging, rewarding and motivating to start a process that will invariably keep moving on and to be aware that I will be able to clear up any doubts or vocabulary blanks in the meantime.