I remember, as a shodan (1st degree black belt), thinking I knew a lot and suddenly Sensei corrected me on something that I never even thought of. Later, I realize that I had progressed to a point where Sensei was taking me to the next level of understanding aikido technique. I had learned the basic techniques but was raising my shoulders when performing certain techniques. This is because I was using muscle power instead of "shuchu ryoku" (concentrated power). It took me close to two years to get rid of this bad habit, even to this day I catch myself sometimes shrugging my shoulders and using muscle instead of shuchu ryoku, but I now can identify it and correct myself.
Ando Sensei says "you start learning aikido after you become sandan (3rd degree black belt). What he means is, it takes until sandan to learn all of the basic techniques, in Yoshinkan Aikido, and be proficient enough at them to not have to think about all of the steps when you perform the technique. It is at this point that you can really start thinking about and practising the small nuances of shuchu ryoku (concentrated power) and kokyu ryoku (breath or timing power).
I have seen many students join the dojo and quit after a month or two, I almost did and I have always been an athletically gifted person. Aikido is very difficult but that is what kept me training, I was determined to do it well.
So, when your frustrated and want to quit, work harder and push through. Your perseverance will prevail and your aikido will improve.
The lesson is this. We strive for perfection, do we ever reach it? Probably not, our technique can always be better. This is budo, this is what forges our character and makes us stronger, more confident and more compassionate people.