I think there are 2 essential requirements for learning a foreign language to a high level as an adult: 

1) time

2) motivation

You can add a few other things like money, resources, etc if you want, but if you don't have the 2 items I mention, you will never learn a language to a high level. Regarding time, it undeniably takes thousands of hours to reach C1/C2. And finally to your question, motivation. Who is willing to devote more than a few dozen hours to a project if there is no reason, no desire, no motivation? Nobody I know.

That being said, there is a popular line of reasoning today, from language pundits like Benny Lewis, which says you need "passion", or "inspiration" or some other exaggerated expression, rather than mere motivation. This is absolutely false. What they are really talking about is merely a higher level of motivation. It's nice to have, but hard to maintain for a long period of time, so people who convince themselves they need this will crash and burn when their motivation drops off.

So it's better to have normal motivation, which you can rely on at all times. Sometimes you are going to be high, and sometimes you are going to be low, but with a normal motivation you will always be able to study and progress in a language.

In my case, maybe the enjoyment itself is a motivation. Last few months I really enjoy listening to spoken English. It can be an English movie, audiobook, podcast... I do not know why, but my ears love it.

I think so, but I don't overestimate these aspects.

And my motivation? I deeply know why I want to learn languages. That's all. Sometimes when I'm tired and I have my iTalky lesson ahead me or I must review my vocabulary or do my daily dose of reading, I just say to myself that purpose and immediately I start studying. Actually I have strong willpower and I don't give up thinks, which is something I learnt when I was really young from my parents. So I don't care if I struggle with language learning today or if I'm worse then my friend... because in the long run I'll win, I'll be the best copy of myself and there is no other end. I do a little steps on that way every single day and therefore I'm becoming better and better every single day. I'm able to undertake inconvenience in order to learn something, which is really important part of obtaining anything you can even imagine, there is usually no easy way. For example I have really tight schedule, because I study at university as well as work (about 20 hours per week). Just these two thinks make my calendar full. However, I want to learn languages as well. So what to do then? Ok let's wake up an hour earlier and learn in the morning before I leave my home. It is not convenient and I cuss every second or third morning on that, but it is only one time I can schedule some language learning, so then just do it. And then I can see around me a lot of people who for example just work and still they don't learn with the same pace as me. Why? Many reasons, usually they don't see a huge advantage of knowing a language or they don't have right habits. It's simple as that.

Sorry if my post is a little offtopic or long :)

I do agree! :) both of them are important factors in learning process. Acquisition and retention of information is sometimes hard tasks to do! Whenever we want to learn something we have to involve our cognitive organisation ,memory ,and our storage system.So,inspiration and motivation can facilitate our learning process.I believe in friends and familie's support!I always get inspired by Watching movies ,reading mastrepieces,listening to music ,and finding my great models and following their ways.