I wish i knew how to train players at first, hurts thinking of all the wasted time on 23yo 4k guards, attempting to jump shot train a center with atrocious JS and JR(who i bought because they had MVP potential, even though they were 21), trying to train a PG and a PF at the same time(wasting some of both their potential), buying a PG to train because i had just sold a trainee, realized he wasn't worth training and sell him for less than half what i payed and more noobish stuff like that....and probably more mistakes i will make and face palm to in the future......that's a little more than one thing, but hard to choose between so many mistakes