Sorry if my answer is a little "weird", but I don't speak German, and in order to understand what you said, I had to translate everything, and I'm not sure it's 100% right.
I agree with you, but not completely. Having some expectations is good, especially when it comes to yourself and your own development. It will help you become better and, in a lot of situations, it will help you achieve quite a lot. It may even make people see you the way you want them to.
The "problem" appears when one has really high expectations of something that isn't always in his power. I can use the same example I used in the article - freelancing.
You can have high expectations both when it comes to what you may be able to achieve and to how those around you will behave and will treat your work.
That doesn't mean everything will be easy. It also doesn't mean you'll succeed. Expectations don't really do anything except motivate you to work for something you aren't certain you'll achieve.
That's why I think expectations should be managed. Believing in yourself is one thing. Having high expectations when it comes to what you can learn and how skillful you are is also good.
However, having high expectations when it comes to success, and expecting to succeed just because you have high expectations, doesn't mean you will. That will often lead to disappointment unless you have a really good plan to avoid failure.
That's why I'd rather keep a balance between expecting to succeed but also being aware of the fact that sometimes things will be a lot harder than I'll anticipate.