You can buy when the price is low and when prices fall and sell when it rises again and you must be able to do this method to be able to get a lot of profit
Buy low sell high is the rules for trading. It also depends on demand and supply. When demand is High the price will also be high and when supply is high the price will be low. You can take advantage of high supply, but in case of cryptocurrency the problem is that the supply is always low because of low mining. Due to low mining bitcoin price cannot be reduced.