i'm a real negative guy with low self esteem, but everytime i've wanted to quit a much loved hiphop element, i just can't. once you geta taste of it, it's there forever.
also, many people are often too judgemental of their own work etc.
try this:
get the first ever shit u did.
put it aside.
keep sketching for another 3 months
get last blackbook page u did
compare with first
notice difference
smile, and continue

keep uppin mate