Your failure is one of risk management. As others have said, have a defined stop-loss before you enter any trade and adhere to that stop-loss no matter what.
Furthermore, a good metric to determine your risk management skills is how long you're holding onto your losing trades. Have a rule for yourself where if you're in a losing trade for longer than a minute, you exit immediately. Set a timer if you have to, but that is how you keep your losers small.
Big losers take time to become big losers, and by exiting your losing trades immediately, you prevent small paper cuts from becoming gaping wounds.