Hang in there. Don't despair.
I know the feeling you are talking about. This occurred to me when trying to learn some advanced sleights (... I wanted to do real magic, you know). I undertook a sleight during my vacations, and practiced this single sleight every time I could, trying to figure it out, finger placement, pressure, speed, grip, anything that would make it work every single time. At the end of the two weeks, I got to a point were I would be able to do it most of the time.
This is when it struck me. I don't think of myself as a natural in magic, but I like it enough that if I dedicate the effort, and persevere enough, and constantly try to analyze and improve my technique, I could learn any sleight.
And that is the thought I have any time a sleight takes more time to learn than I expected. I remember that if I dedicate enough time to it, I can get it. I also understand that I can't rush it. I must take pauses, and let the move sink gradually, and gradually refine the level of detail that is required to do the more properly. If it's not ready to be performed, it is not, and I patiently continue to work on it.
So,
Hang in there,
Don't despair,
Set yourself small goals,
Give yourself time to learn properly,
Give yourself some time to rest, don't frustrate yourself insisting to doing it over and over in a single session,
Be patient,
Dedicate yourself to it,
Be passionate about it,
Enjoy practicing... because you'll spend more time practicing than performing for others,
And practice, practice, and then practice again...
You'll get it eventually.