In my experience, you don't have to be smart or hardworking to learn a foreign language. The most important thing is the amount of exposure to content that you enjoy. Over repeated exposure, your ears will become familiar with the vocabulary and the core grammar of a language. And over time, they will become easier to use actively. 

Some tools that have worked for me:

A Chrome extension called Language Reactor (free). It lets you view YouTube and Netflix with subtitles in both English and Korean at the same time. 

Bilingual books with audiobooks. There's a series of bilingual books -- English books with Korean translations on the facing page -- that come with audio recordings. Listen to the audio while reading along with the book. 

Here's an example of one.

https://www.ybmbooks.com/book/book_view.asp?seq=1880

You may first wish to read it in Korean (while listening to the audio), then in English (while listening to the audio), then just listen to the audio without reading along.

After several of such books, you can move to the next step: listening to an audiobook in English while reading its Korean translation.

가장 중요한 것은머리 쥐어짜서 공부하는 것 보다는 즐기는 내용을 듣고 읽고 보기.