I was curious if anyone could enlighten me as to how people calculate when it is more efficient to exit a position once it has turned against you and re-enter at the new lower price ? I see a lot of people using stops at various levels, but there has to be some mathematical way to determine that at a certain point once your losses on accumulated profit have exceeded a certain point it makes more mathematical sense to exit and reenter. And I know that if you are in a position and up 30% setting your stop at just above break even doesn't make sense. I would think to a certain extent slippage, commission and opportunity costs (i.e. you exit at $100 only to end up having to reenter at $100) would play into determining this. Any enlightening ideas from some of the wise birds on here ?