I do not believe anybody can predict the bottom. You buy when there is a significant discount from the peak. You sell when there is a significant increase from the bottom.

Means if you pay $100 for something and it appreciates to $180, sell, regardless whether it will go to $200 or not because you already profit. When it comes down from $200 to $120, buy, regardless it will go down to $100 or not, because you already bought at huge discount.

Most people wants to buy the the lowest ever bottom and sell at the highest ever peak. They want to be fortune teller. Predict? Why not go casino play big/small?