It would be difficult to catch falling knives during btc's dips. The best way is to cost average. If you have a certain amount you are willing to trade to btc then don't change is all at once. So in case the price falls more then you can buy again. Regarding to those people who buys high then hodl and sell low. I think these are people who doesn't yet believe in btc for the long run. Causing them to panic sell. Because if you fully believe in btc's future then you wont have a panic sell attitude for every dip because you believe that it will bounce back sooner.