English or Korean ?

They say Korean is easy to learn for Japanese because of a lot of similarities to Japanese. I have just started studying Korean. I am still a beginner. So far, to me, Korean is much harder than I had thought.
The more I work on it, the more I come to notice its difficulty.
I thought about the reason over and over why I feel differently unlike most Japanese feel.
Now I have reached to one conclusion. That is, I do not understand Japanese well. This must be the core of my problem.
I am a native speaker of Japanese and I have even worked as a staff member of correcting essays for high school students who were trying to pass college entrance exams.
However, I have never paid attention to what I say in Japanese and there is no knowing how Japanese is composed of.
That is what native speakers must be. The same could be said to other native language speakers.
Therefore, I decided to pay more attention to and become more conscious of the usage of Japanese in order to improve my Korean.