When the prices are falling I can see red hot sale. That is the time to take advantage on the lower price of coins buy as long as i have money to invest because i know that it would be a good buy and just hold it till i reach my target percentage then sell.
When the coin is going through dumping stage, that is the best chance of grabbing more and more of it because after every hard dump, coins do pump high leaving al investors in ecstasy. There is no need to miss the chance if the respective coin is bitcoin because they are now about to touch 5k dollars soon.