So what does drawing a line in the sand [to sell after a decline of] 50% do for you? It prevents a larger decline, but it can also prevent a very satisfying recovery. Here’s the bottom line: There is no magic line in the sand. That is, there is no arbitrary pullback (small or large) that should itself trigger a sale. The best time to sell is when your long-term view of an investment’s intrinsic value is such that today’s price doesn’t offer sufficient reason to remain invested.