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
I'm in agreement with your opinion, most altcoin we see won't be around in a couple of years. It takes a whole lot of effort to keep a project running. Some developers would abandon the project when they face set backs. So in my opinion, it's best to only hold those coin you're certain would do well in the long run.