Hi… Actually this is the problem of 95% traders I guess who have lost money including myself. But what we need to realize is that “Trading system” we use needs to be first thoroughly back tested, then tested in live mkt with very small positions say 2 to 3 shares max to get the feel of its credibility in real environment. Have we all done this… If yes and was successful that time, then problem could be our bad position sizing, risk reward unfavorably placed etc. Most important question is whether you were comfortable, relaxed after getting in the position or were constantly under pressure to get out? Did u make ur entry with so much stringent criteria fulfilment that exit is a cakewalk…??
In zerodha varsity karthik sir has mentioned very well about position sizing and ways to hedge a portfolio. What “trading for living” will add is how we save ourselves from sharks bites and pirhanas of mkt… Give it a read for very relaxed position taking 
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