Investing in cryptocurrencies is risky but it is even more risky when one invests in an altcoin. If your friend jumps into an altcoin without having a good knowledge of crypto-currencies, he might have a big loss, but since he jumped into Bitcoin, it's risky for him and won't hurt him too much. So now you should explain to him that if he wants to get something good from bitcoin he has to keep it for a long time, if he sees some losses here he can't panic and sell them, he has to hold them strongly and if he can hold for a long time he can get a good profit from here. And since he is very interested in Bitcoin, he can invest in Bitcoin by following DCA . And of course he needs to use a secure wallet to hold his bitcoins.
Not all altcoins are equally bad, there are some that are much more volatile than bitcoin, and the project is doing very well, entering into new partnerships and constantly developing, and I believe that such altcoins can give significantly better returns than bitcoin. But at the same time, I will invest less in altcoins than I invest in bitcoin, because altcoins will always contain more risks than bitcoin. Safe storage is also very important and the first thing to do.
It is important that we know what we are doing and must know what coins we are about to invest with. Although investing in altcoins is too risky but somehow, being an investor doesn't just consider buying a single coin as it is best to have another one or more. I have Bitcoin which I spend 60% of my total capital while 40% on altcoins, I believe this is a great idea (IMO). BTC, ETH, and BNB - I think it is all enough for me.