Altcoins don't just follow in bitcoin's footsteps, but also multiply this effect many times over, especially when it comes to falling. If bitcoin falls by 10%, altcoins can lose 30-40%. There is a flip side to this effect as well. When bitcoin grows by 50%, altcoins can grow by 200%, but they also quickly become cheaper after such growth, so you need to sell quickly, otherwise all the price momentum will disappear as if it never happened.