On my Loser List for March 3, I said BZH might be a long, if it showed some strength, with a stop about 170. On the 4th, I bought after it had risen above 171. I looked at the chart a little more, and got a little spooked by the daily ATR, or average true range of 5, which basically means that 50% of the time, the stock's movement from high to low is >5 points. I thought, jeez, if I put my stop at 170, I'm gonna get stopped out for sure--so I put my stop at 168. Well, you know what happened--BZH went down to just below 168, stopping me out just above the low of the day, and then on Friday climbed to over 175.
Now, this is NOT a bad trade because it was a losing trade. It's not a bad trade because I essentially bought near the high and sold at the low. It's not even a bad trade because it ran down to my stop, then turned around and rose above my buy point. No, it's a bad trade because 1) I had a sound plan based on a sound methodology, but 2) I didn't follow my plan. Let's look at the hourly chart below, mostly because that shows the support best. Remember that I was looking at the chart on March 2 and buying on March 3. (Note also that the ATR on this chart is the hourly ATR, not the daily)
courtesy of stockcharts.com
Based on the chart, I think you can make a pretty good case that about 170, or maybe 169.5, depending on how precise you want to make these numbers, was resistance, based on 2 prior highs, and then had become support after the resistance had broken. There are good reasons to be respectful of the ATR; certainly, if you consistently set stops within the daily ATR, and hold for a couple days or more, you have a good chance of being stopped out just by daily fluctuations. However, if that's the case, then a realistic stop outside the ATR might have been 165, or even 160, but 168 was just pulled out of the air--in fact, it was still within the ATR.
In retrospect, if I had stuck with 170, I would have still be stopped out, but at a loss of 1 point rather than 3. And if I really thought ATR was an issue, the stop should have gone lower, probably 160--although that would significantly change the risk/return on the trade.
The lesson: Plan your trade, then trade your plan.