Because some altcoins for now it have a enough value that you going to trade it, But if you going to buy some altcoins and you know that this altcoins you buy it will going to pump maybe you will be going to rich.
I recommend that do not focus in 1 altcoin much better to have atleast 3 to 5 altcoin that has potentially increasing its value and mostly those altcoin is on the top 5 in crypto currency market but much better to have altcoin for short term trading to make faster income.
Actually im just trying to buy some altcoins, But now as you said if im going to buy altcoins so the top 5 altcoins or maybe the altcoins have some potential to be sure that have get some enough or have a big income that im get.