How long is "forever"? I've been actively studying for 5 years with 10+ years of immersion and I still make mistakes on certain N4 grammar every now and then. To me expansive immersion is the only way to really make things "stick".
You can memorise rules, but using them naturally comes from lots of exposure and practice in real situations. I also feel like a lot of the grammar you get taught is oversimplified and doesn't fully reflect how it's used in natural, spoken Japanese.
This is just what works for me. Don't get too discouraged, learning any language is a long and difficult process :)
Bro, you r not stoopid you're experiencing something every serious language learner goes through especially a language SO MUCH different from English. The fact you are doing both N5 and N4 content shows that you're dedicated and persistent.
Even I am doing both N5 and N4. You are not alone dude. Do you even know that many learners don’t even make it that far ( by far I mean N4 ). You might know individual grammar rules but sentence construction often requires flow, which takes so much of practice. You do tons of questions which are correct, and then one question wrong, all your happiness in the pond. it can feel discouraging and thats common, its a sign u r leveling up.. So never give up bro
something i'm doing right now is not adding new materials to my japanese basics schedule (which also prevents new words from being added to words for japanese basics), so i can focus on only reviewing terms until i feel ready to progress with learning
Me too, right now. And also several time before. So, first advice on that: Take a break Second advice: Try something new
App like renshuu (And SRS system in general) are really good to make you work everday mindlessly and it's really good for language learning but at the same time, it really just consume your energy and motivation. At the beginning, it works because you will have some fast progress. But the more you overuse it, the less it will work. And past a certain point, well "and Renshuu has been involved for the past couple of months religiously.", yeah, it's that feeling and no real sense of progress.
So take a break and get rid of that feeling first. Because, on one side, yeah, it's probably true that you're not making as much progress but at the same time, it's also just because you're a bit burn out. And don't think you're giving up or slacking, seriously. The few times where I did take a big break (like 1-2 month or more) are also the few time where I ironically made the most progress. It's a bit like I learned too much at those time and my brain needed time to organize things. Renshuu (and similar system) doesn't have the concept of break at its core. If a word need to be studied on sunday, you have to study on sunday even if you're currently burning out and it's mostly pointless to study in that state.
Alternatively, you can also try something new. There are no perfect method that cover everything and there are no universal method that works for everyone. On that note, there's also no perfect grammar theory that explain everything perfectly and make sense for everyone. The JLPT one use one grammar framework for example but it's far from perfect. And can even be harmful in the long run. But there also people that managed to learn japanese only through that grammar. So unless you try, you won't know if it fit you or not. Same for the different methods. Also, just trying will get you out of that "state". Just because it's new. It's a bit stupid but it works. And who know, you may find your new favorite method. At least, it's like that for me. Part of learning japanese is just finding and testing new method or explanation that work for me, do it for a certain time and come back to older method once I feel bored or start to not feel progress anymore.
Anyway, that's my case. But the most important part, again, is: "Me too, right now. And also several time before." If you need to remember only one thing, it's that part =p. It happens, that's normal. Doesn't mean you won't be able to speak japanese at some point.
I consider it as the learning process doing its job. You aren't familiar and are prone to mistakes as a matter of course. If you make mistakes, be sure you'll eventually get it right. The more mistakes you make build a more concrete understanding of the topics you're learning; The more it cracks, the stronger it gets, and the more pride you can take in it. It's not always fun, it's progress, and part of the process. Keep it up! If you want to.
you're experiencing something every serious language learner goes through especially a language SO MUCH different from English. The fact you are doing both N5 and N4 content shows that you're dedicated and persistent.
). You might know individual grammar rules but sentence construction often requires flow, which takes so much of practice. 
