This is such a basic , okay let us say this statement is correct , how are you going to know that the price is down or not? because as we can see at the current situation of the market , although we can say that the price of bitcoin goes down it does not mean that it will not go down . You should know the factors that affects the price of bitcoin, first is reputation , which bitcoin already have but sometimes because of black propaganda it decreases , second the volume of investor , you should know why there are investors that are pulling out before investing. theses are just basics , the bottom line here is you need to conduct thorough research before investing.