Lots of factors can be looked into why crypto price will fall on a certain period or worst scenario, a whole crash; news, FUD, whales movement, triggered panic, profit taking, upcoming event etc.

How to predict on it? Even how well and good the analyzation, it will still a speculation so in other words no way it can be predicted. If you asked that question as reference if you want to invest or not on a certain coin then I will say that you must take the risks. This is how investing on crypto works.