It only works when a stock gets oversold due to irrational fears. That is not always the case. Sometimes the fears are completely rational. I'm not saying which is the case here, l'm just saying that you need to understand why. If simple rules like this always worked we would all be millionaires.
Actually simple rules can be right but hard to follow. Yes sometimes selloffs are valid. But often they are not. People don't buy because it's always easier to follow the herd. The key if you're going to fight the trend is to buy gradually. It is impossible to hit the bottom exactly.