Because bitcoin depend on simple demand and supply low it is so risky and price can change more than 1k from night to night soyou will not know right time to buy low and sell high
Correct, we can not predict when bitcoin value would increase or when will dump, but you can make current value as your basis if you feel that value are lower in your apetite just buy it and sell when the value is much higher than value at the times you buy a bitcoin.