Ever since I started trading, I was fortunate enough to learn that it`s vitally important to know how much you can afford to lose of a trade. We all have trades that go against use, whether it was incorrect analysis, erroneous event that brought the markets down. What ever the case maybe you need to set a limit on how much you are willing to lose.
Here is one of many videos that has helped shape my money management as it relates to trading. You can see where this is reflected in my TSX Today segments on my website.