we sell when the price is rising and we buy the price sat down, simple not, just we need to know when the price goes up and when the price falls because it's hard to predict we can only monitor it trerus continuously until the price rises
You are right about the buy and sell thing but mostly, those people who do not need a stable income monthly or daily does not really require to sell their coins, holding will always the best way to earn profit because the value of bitcoins is increasing as the time goes by.