Cryptocurrencies have long started its course in this world, it's just started gaining this much of attention recently. One more thing is that when you said hold, it seems that you are referring to all coins that someone is holding. So, I will just say that holding is not the best option for all kinds of cryptos. Some coin is better holding for a long-term and some are better if it will only be on short-term. They are frequently suggesting to hold because their assuming that the coin you are holding has great potential and has huge possibility that its price will recover greatly after the dip.