Anybody who sells his Bitcoin because there is a drop in Bitcoin price doesn't have any knowledge about Bitcoin. That person only invested in Bitcoin because he/she saw a testimony where Bitcoin has made some people rich, and the person thinks that such a thing will happen if he/she buys Bitcoin and holds for a short term. By the time the person accumulates his Bitcoin, with the aim of getting rich soon and when this doesn't happen he/she will likely sell off his Bitcoin even though he/she is at a loss because what he/she was expecting from his Bitcoin investment did not happen.
This is enough reason why I keep trying to convince people into having even the slight knowledge about Bitcoin not referring to the technical aspects of it but first considering first on how to buy and also when to sell Bitcoin, like what strategy to apply, is it by DCA, Buying in lump sum or by buying the DIP choosing which is best to accumulate more efficiently. Also knowing where to hold Bitcoin after buying from the exchanges, having the knowledge of holding huge amounts of Bitcoin In an exchange is risky and should be transferred into any of the hardware wallets.
Mr @JayJuanGee dropped a tool
here which may or may not be that efficient enough to calculate based on the 200 - Week moving average on when to buy and also when to sell.
Lastly, knowing that Bitcoin investment is usually for a longer term and patience is needed even when the market falls in bearishness, this is understanding how volatile Bitcoin can be.