Before you even place the trade, you have to have a set price of where to get out. If buying a breakout of a trendline, Protective stop can be under the lows of the bar you buying above, lowest low of last three bars, if a traingle it can be mid-point of triangle or as far away as other side of triangle. By you saying you have huge losses tells me you don't have a set price of where to get out. As far as where to take profit, what plan do you have for that? Do you take 50% off at certain point and let rest ride for bigger profits or do you allow all to ride? Have to exits well planned before putting on trade.
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.