The simple rule is "buy at the bottom and sell at the top". But i don't think this applies to all coins, it only applies to solid coins like bitcoin, ethereum and the likes, because they have stood the test of time and would surely find their way back up. But most of these new coins, if you buy at the bottom, the price might still go lower and keep you trapped there. so it is better to wait and see a clear move up before you get on the train to avoid fake outs.
You said it right.
Most of the new coins, if you have bought it, usually it's already the top of it and then the next thing that will happen is mostly a dump. The dumping of most investors that bought it during the sale is about to happen.
All of them will be chasing for the profits and wouldn't actually care with the vision that project has. This applies for most new projects with or without potential. Lucky if the project has the potential as it can recover afterwards but mostly don't.