For altcoins, buy low and sell high, and you will make a profit. Although this statement is correct, it does not go for all coins. Some people think that when the market rebounds, their altcoins will rise with it. But the result was leaving the market at a loss.
So choose wisely and follow up the project. See what their developers are doing, or just hiding behind the prevailing saying.
It is of a truth that not all altcoins will recover when they dump in price, but one needs to know what causes the dump in price, that is, if it is the market, the team exiting scam or the team working in the background where they are paying full attention to their developments. If an altcoin dumps as a result of the market, it will rebound if it has something good to offer which will draw back more investors to it. If it is as a result of the team exiting scam or abandoning the project, there is every tendency it won't work out again. Now the most tricky part of it, is the project or altcoins whose team are working out something while paying little attention to price, most of the times they come back huge and better, because what they have built over time is worth it.
So therefore, before thinking of holding a coin or token, do well to know the team stand on that project and if they are willing to work it out, because the success of a project depends on them which in turn leads to price growth overtime.
Lastly, knowing when to take profit is also important whether long term or short term.