There are a lot of experienced traders out there, who purchase the coins during the dips and sell them when the bull rally occurs. Their success rate can very from person to person and also luck plays a major part. As we know, it is incredibly difficult to predict the future prices of Bitcoin (and even more difficult to predict that of the altcoins).
Predicting any of these markets is next to impossible and also the time comes when most of the holders are in loss. Last time when we were enjoying the bull runs there were peoples who bought even at that price and now are holding that amount to have some profits by these coming bull markets so the profits would depend on how you judge your coins and how long you can potentially hold the coin.
Even when the markets are down, there are peoples who buy and sell instantly to make some profits from the coming markets so we can't assume that when the markets are red each of the investor is in loss. There are strategies which would be applied upon to have profits in each market condition.