Failed Prop accounts this week - mistakes made!

I will start with one and only mistake I made, which cost me 5 Express funded accounts with lot of money, which I could have drawn. I overplayed my hand. I entered with 2 NQ contracts and when market made a move in my direction I doubled my position to 4 contracts and then the damn thing just chewed me out, in one ranging area I've lost all the money and all the account I've worked for for many many days. Greed and impatience cost me $1000 of hard cash (cost of the accounts) plus thousands of dollars of earned but unclaimed money, which I was accumulating...

Student of mine called me so happy and excited, saying she has completed here combine and made $3K. She shared the screen with me with so much pride and excitement- guess what I saw? She was making trades in the old account which she busted weeks ago. In the mean time her new account was charged 2x$49 was just sitting there with zero balance.

Another student of mine, keeps loosing his express funded accounts. He opens 5 at the time, maximum allowed. passes combine with his eyes closed, pays for upgrade to Express FUnded account, and then within days becomes arrogant, complacent, overly confident and blows all accounts to shit. Reason - goes into a trade with too many contracts, then tries to revenge trade, end result is always the same - bust! Mind you this guy know the market, knows how to trade, knows it all except position managing....

Another student, I watched in my trading room several times... He gets into a position, he is up 50-60 points and fails to trail his stop, twice turned hugely winning trades into a loss. Once again over confidence, arrogance is killing talent!

Last one I want to discuss, is forever in his combine. He scalps perfectly positioned winning trades (gets out too soon with just a few bucks) but stays much longer in a loosing trades....

I have found my solution to my problem, I've figured out a perfect position size for $50K account, have you found your solutions?