The issue with placing stop orders is often times what algorithms/hedge fund traders do is what's called "hunting stops" and shake smaller traders out of their positions before the stock goes higher.
Look at this way everyone's looking at the same information, so if you know where to put a stop they know too. Your stop gets hit and you sell, they bought the shares/contracts you just sold, they make the market move higher while you're sitting on the sidelines.
Also, the data for every order you make is sent to them by your broker, so they know where your stop loss is and what you're likely to do when it's hit.
So my recommendation is to learn to trade with a mental stop and don't set the stop on the order. It takes discipline since you can get married to a position and get out later than you know you should've, which could mean a bigger loss. But whenever that happened, I always looked at it as that's what I get for not sticking to the plan and taking the small L.
Over time you'll get strong enough to win over greed and close the order.
