While the method works most of the times, it can fail from time to time; so, good that you made profit, but buying something that fell 4%  and using Luc's method is quite risky. Before you buy you want to see a big drop, especially for smaller coins! Things can drop 50% or more, so if you buy after a 5% drop (with a 5% expected return), you'll get into trouble when one such trade fails, burning the profit of tens of such trades!