Oddly enough, I have learned that learning a language (in school) is great for reading and writing. However, it is not practical for everyday usage. For example, I have studied French for a number of years in school, during my youth. We were taught the proper and formal way of speaking. However, the average Parisian is possibly not as formal while speaking. This causes a rift in communication sometimes. 

I could tell you similar stories of me and Spanish. I have quite a number of hilarious ones actually. It seems as everytime I visit a Spanish speaking country -- I make another mistake. But, that is apart of growing and bettering oneself. Making mistakes and learning from them.

This is the same for people whom learn English as a second language. Sometimes, they are a tad too formal while speaking or have learned grammar rules which have exceptions. Because they are not acquainted with these exceptions -- they tend to become frustrated. 

I am available to speak with persons desiring to learn English most times. I find it a great joy to share my language -- which is apart of me. I strongly believe that with practice, one will be able to better their language abilities exponentially.

correction : We all have learned English for more than 8 years.  So then, why can't we use English correctly, or like natives?
I have often discussed this with my fellow partners, but no one can give a clear opinion.

> we all learn English for more than 8 years ? why we can not use English correct and native ?

Legend Steve Kaufman talks about it here, not sure where, you need to listen to all 5 or so parts:

https://www.youtube.com/watch?v=CIgjwJck1Ho

I am studying Mandarin, and I like you must practice speaking (练习口语 )。

Thank you Isobel . What you said renewed the interest in English of me !