To butt in (excuse me): the main difference between knee-jerk averaging down and waiting to buy when the stock bottoms is exactly as you indicated.
Whatever fundamentals/news/reports/etc. that caused the drop have now had time to do the damage they're going to do. The stock settles, it begins to move up. Now average down.
All that is needed to make a happy life is within yourself, in your way of thinking. -Marcus Aurelius