It looks like selling your crypto for money when they are profitable is more safer than holding them for long, my point is only very few coins are worth holding for many years, if you still doubt about this go on coinmarketcap and look at most coins that came into this world in 2018 many of them have no volume again, the shocking one to me is gowithmi, a project that my elder brother praised so much at the time but today it's volume is not up to 50k, many projects will face same fate, be smart
Of course, both BTC and ETH are prime movers, so you really need to hold them in order to make huge profits in the future. 2018 was really bad for the altcoin market, even ETH's lowest low was in 2018, but they have gain so much and for sure if you have stayed with them, you are very profitable even today, even if the price is way below their last ATH. And yes, maybe your brother just hold some shitcoin that's why it didn't do well, so we really need to invest on coins in the top 10-20 marketcap.
I have never heard about the project, gowithmi, that the OP mentioned. But it is true that a lot of alts and tokens created way back in 2018 were long dead already. Very few are still surviving but definitely BTC and ETH are the frontrunners in this market. Because for one, the dev team behind ETH is really doing their job to innovate this network. It may have high gas fees but the team is in continuous pursuit to improve their services, whereas, most tokens were already abandoned because the main interest of their dev team was to rip off those buyers as much as they can.