That sounds logical to me. Now, as I switched to get every group repeated it is a lot easier to copy everything without problems. So I will try to work me up to 10 characters and then start with 2 other characters and work up to 10 again. After that I will try to combine 5 of the first set with 5 of the second set and so on. The problem is, that it is relatively easy to copy a set of characters, when I know which characters could come. So I have only to concentrate on those.
From all the replies I figured out, that there are probably more ways and most of them could bring me to success. So I will try different approaches. I think every repetitin in listening to morse code brings my closer to my goal.
I was a little bit frustrated, because at the beginning of my journey, I progressed quickly by just learning to recognize every character and be able to send every character. So I thought to me: "that's easy. Wouldn't last long to be able to make QSOs. What a fail
So I recognized, that I have to be more patient.