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I’m not a huge fan of this quote from Paul Tudor Jones. Some of the best investors of all time have made a fortune adding to temporarily losing positions. And while this is true, it is equally true that the worst investments and the worst investors have added to losing positions, not knowing when to call it quits.

Let’s use Twitter as an example. If you bought 100 shares of the IPO at 26, and added 10 shares on each of the 25 times the stock closed at an all-time low, you would have tripled your original position, and would be down 30% on your investment.

Thinking a stock can’t go any lower, and then acting on that intuition is a strategy that will leave your account dilapidated. There’s a lot of ways to lose money in the market, and 99% of investors who continually lower their cost basis will do just that.

Possibly in individual stocks. Less so in ETF’s which are a basket of stocks. This would be a very profitable strategy in SPY, QQQ or any other index based ETF since any starting point you care to name through to today.