...’Buy at low and sell at high’ is the simple way to ensure profit from investment. It doesn't mean that you need to buy at dip and sell at top for taking profits. Don't look at the price much if it falls after your purchase. Just wait with patience.
Those who gained experience in 2017 are no longer willing to turn from traders to holders. As you can see, they had to wait 3 years before the bitcoin price returned to its ATH. Therefore, in any case, it is necessary to carefully monitor the price change, so as not to freeze your money for such a long period.