The academic instruction was crucial for me. No matter how much I listened, I was never going to really understand the difference between unidirectional and multidirectional verbs of motion until it was explained in a way I could really grok.

On the other hand there is quite simply no replacement for hearing and speaking with native speakers of the target language. I taught quite a few English classes and there were often Ukrainian teachers who spoke English flawlessly, but for whatever reason students who only learned from non-native English speakers were at a clear disadvantage compared to those who also had native teachers, and everyone was at a disadvantage to those who had practiced in an English speaking country.

I worked with tons of people who lived in eastern Ukraine for years and never learned Russian or Ukrainian beyond a few phrases, I really do think it takes dedicated instruction combined with tons of practice with native speakers to really make fluency happen.