Yes investors shouldnt invest in only one coin. Everything can be happen in cryptospace. For example i am holding eth and btc. I can hold only bitcoin but i dont want to invest in one coin with all of my money. Also altcoin investors have to be more careful while doing their investments. In may we remembered some coins which did 5x 10x 20x but these coins all red now. So we have to invest more than one coin. You are very right about that point.