it is the risk management plan. you invest something and then speculate the price will go to 1 million dollar and then you wait until then. but nothing is stopping you from selling when price is lower. it may actually be a good idea to sell something when price reaches new ATH.

of course a better course of action is to buy in the dips and sell on tops and then buy back in the next dip. for example when price reached the ATH of $4900 you could have sold some small portion of your stash and wait a while till price bottoms out then buy back the same portion you sold and keep the profit in fiat for yourself. although some people keep their profit in bitcoin meaning they buy even more bitcoin after the dip. you sell 10BTC and buy back 14BTC