I thought about the comment by Kenichiro Mogi, what is about the education of English in Japan. I guess we can have two types of motivation to learn English. One is the one that is given from outside forcibly like "Unless I learn English, I can't get any good jobs". The other is the one that is flooded from inside like "I want to learn English and work globally". If I think this idea more seriously, our motivation might be from a kind of 'hybrid' of these two types and be born as one in ourselves. And, in my opinion, the latter which is 'inside' from myself lets us keep on learning English.
Going far from Mogi's opinion, I had learned English from 'outside' forcibly when I was a student. I couldn't find why I had to learn English. In other words, I could have no chance to use that knowledge of English as the communication with native speakers. The purpose was very vague so I stopped learning if I ended studying in schools. Now I write my journal and talk with a lot of friends on Discord and WhatsApp. It's from when I graduated from the university and met them in my private life. I can say that I have got motivation from 'inside' to tell them my opinions.
Of course, everyone has their style. It can happen that the person who learns English from 'outside' forcibly can master English. But, all I can say is from my experience, I think the motivation from 'inside' is quite important. Language is for communicating with others so we can treat the joy of telling someone our thoughts preciously. The joy of doing trials and errors, also the joy of getting embarrassed and doing progressing... It is a clue to keep on learning English I believe. But this easy opinion might come from the fact that I am not a serious business person who has to use English severely...
I told this to a friend of mine on LINE, and she told me some interesting information. Now there are some students who can't say their opinions on debate/discussion at their universities. Even if they are allowed to say their opinion in Japanese, they can say nothing easily. This means that they haven't been living without the chances of declaring their opinions. So, besides learning the technique of learning English, learning to make their opinions and tell them are also important. As Antonio Inoki says, 'becoming foolish' and getting shame by saying our opinions, and also treating other people's ones. That must be important.