If you keep the etherium or bitcoin, you can forget about them for a few years, as these are reliable crypto coins. But if a new generation coin suddenly appears with very great prospects and you do not have time to purchase it in time, then you can lose money.
I will probably add litecoin to the mix of coins that you can buy and forget, this is precisely the reason why most of my money is invested in those three coins, I do not want to bother to look at the market for hours every day and trying to figure out when it is the best moment to sell or to buy, I'm not going to bother doing that because simply I do not have the time to waste looking at the market all the time.