When bitcoin rises, the altcoins keep the price and if when the bitcoin falls the altcoins fall even more. Why do altcoins usually follow bitcoin?
Because they move on the same technology and bitcoin is the father of all cryptocurrencies. So when this crypto (bitcoin) go down, other digital token or altcoin tend to decrease in value as well. When bitcoin goes up, its likely the move up at the same. And thats how crypto works.