Bitcoin indeed often decreases and increases quite sharply.
While Altcoin influenced by the price of Bitcoin. When Bitcoin rises then Altcoin also go up. If Bitcoin goes down then Altcoin also goes down.
But Altcoin's decline and rise is not as extreme as Bitcoin.
I have a different analysis where altcoin fluctuations are more extreme than bitcoins that always get futures correction, too often we see red altcoin under any circumstances, we only see altcoin stabilizing itself if bitcoin prices are inserted in the upper limit correction. This view is exacerbated by the tendency of the trader to always move from one coin to another.