Why can buying low make money?

The market will always have a "spring rebound": just like a ball hitting the ground will bounce back, if the coin price drops too much, there will naturally be a rebound.
Avoid chasing after price increases and selling during drops: The most common mistake beginners make is to chase after a rise and run away when there is a drop.
Large funds also love to buy low: major institutions prefer to secretly build positions during a downturn.