the science of learning grammar & why immersion fails

I see basically 2 recommendations for learning grammar on this subreddit and generally online:

pick up a grammar book

and

just immerse more

"pick up a grammar book" doesn't work because there's no repetition or active practice to it. You read through a rule and maybe understand it and a week later you forget it again.

So the answer is "immerse to get practice" right? Not really.

Our brains don't like to do hard work. In most cases we can infer the meaning of a particle by just looking at the rest of the sentence and context. We're missing focus.

My own experience after a year of doing input every day is that I could not speak at all. Not even the most basic sentences, despite understanding a lot.

There is a nice 2016 study that compares scenarios for learning the english grammar concept of "had":

exposure only - here students work through a bunch of sentences like this: "John had his tires changed"

exposure + highlight - the relevant grammar part in the sentences was highlighted like this "John had his tires changed"

exposure + highlight + explanation - same in addition to the relevant word being highlighted, they also got a theoretical explanation of the rules for "had" first

group	output test result	comprehension test result
exposure only	10% correct	58% correct
exposure + highlight	27% correct	61% correct
exposure + highlight + explanation	37% correct	69% correct

The study above is a nice illustration, and the general takeaways are backed up by meta analysees like this one and this one. Generally this concept is called focus on form.

The takeaway is that if you're doing input, you need to make sure your brain explicitly works to decode all the grammar info in the sentence. Translating the meaning of the sentence is not enough.

I personally also use custom flashcards like this because comprehensible input is random and I prefer having all my knowledge in an SRS.
You can add these in during sentence mining with anki or use custom software.

grammar card from https://www.langkit.app/

Comprehensible input is treated a bit like a mysterious religion that is the answer to everything. Half the question on this subreddit are about "how to immerse". Any answer without caveats to that question will always be wrong. Language learning is very well studied and if we get more specific about the problem we're trying to solve then we'll have a much better time :)