Well I'm not a lover of altcoin, that is why I always avoid investing in altcoins, reason been that altcoins sometimes is very difficult to predict, but I will advice if you're buying altcoin you go for those top altcoins like ethereum i think the future of ethereum seems bright and is good for long term holding.
Altcoins are not guaranteed for their profit but still there are some altcoins which can give you a huge return like Ethereum, Solana, matic and BNB and there is no doubt about their success but if it sometimes declines then it does not implies that it has lost its value forever but as it is the part of crypto so ups and downs are common.
Buying altcoins is not a bad idea because there are experts who are regularly earning through altcoins investment but finding out beneficial coins is very difficult among thousands of altcoins. You can choose Ethereum for a longer time and Solana is also performing well therefore altcoins are also worthy but not every altcoin is the same.