My whole life is consumed by this feeling.

I feel like I should already have achieved something great, yet I don't explicitly think I'm special, although feeling like this and letting other people know about this constant irking feeling might understandably lead them to think that I think of myself as someone special or superior to them, especially when talking to people who haven't experienced this kind of push and don't have these kinds of aspirations.
I think that in my case there's a healthy part to it and there's an obsessive, blown-out-of-proportions part to it, based on the healthy part. And it's not easy to tell, where one ends and where the other starts.

The most dreaded thought to me is the thought of mediocrity, me being just another working bee as someone put it in the comments, with no power, ability, skills, and certainly no destiny to build or do something great.
What "something great" is, I didn't really outline it yet. Maybe this should be the first step towards actually starting a project that matters.
I cannot relax. I cannot let go. In my life it is rare, when I can just kick back and relax and enjoy doing something that is not the next step towards something big.

Whenever I'm left alone with nothing to do, the feeling of guilt sooner of later overwhelms me, I cannot have a breakfast without my thoughts rushing. I just keep thinking about what I had done wrong or why I haven't achieved anything of significance in my life.
For one part, there is this feeling that I already should have achieved great things and this feeling implies that I should actually be able to achieve great things, and therefore that somehow I am destined to achieve great things.
Then rationally I know that I am not special at all, but I can be. I know that things that I consider great can be achieved by just people like me, because I know people who have achieved great things. And that there's no destiny involved, just hard work and a lot of skills which can be learned. The thing that is special about these people is their attitude.
The only times I came close to feeling relaxed and being able to kick back and relax, were times when I've felt that I actually had something great going on in my life, something that I've felt could go somewhere, something with potential.

I consider the notion of potential one of the greatest things in life. I would even go as far as to say that I value potential more than I value actual results, more than I value potential realized. Potential is the start of everything, potential contains everything in it, nothing is determined yet, nothing is sure, but everything is possible.

And I think I'm afraid of stepping out of my zone of potential into the real world, because out of the infinite possibilities, I have to choose one, I have to choose a direction, _one_ direction and go there, knowing I will probably never be able to go back. And take directions after directions, and from the abstract notion of being everything at once, out of all the possibilities, I have become only one path, one string of life, that either becomes successful or withers and dies.

From the place where there is no meaning to failure or to success, to certainty or to uncertainty, to decision, because everything is in there all at once, and there is only excitement and anticipation, to the place, where I might fail like many people have failed before.

For now I try to focus on doing things I really like, things that deeply excite and interest me, things that matter to me, and I try to put the maximum amount of effort into doing those things, and now I just have faith that out of these things a project will emerge. And that as long as I can find things that excite me, there will always be a project in there somewhere that's worth doing.