As usual, I really have to agree with Jun in this respect. I've been doing aikido for some 4.5 months now, and I have never once found myself frustrated to the point of quitting
The only time I ever considered quitting was one Saturday morning when I simply couldn't keep up with the class, having to bow out for water and goto the bathroom (I got queasy) almost every 5 to 10 minutes... I sat in the bathroom trying to hold down breakfast thinking perhaps I should quit so I wouldn't have to endure this shame any longer, because it was too hard, than I remembered something from Kodo:
"A student of mine once told me: Aikido is much harder than I thought!
I don't recall telling anyone it would be easy."
At that point I realized it would be even more shameful to stop training.