I guess that smart people analyse the situation and then decide to buy, sell or hold... it really depends... if you are beginning you need to check if the price is actually low and if the project has chances to succed... than you decide if you buy or not...same with selling, but the best thing is not to sell everything at once... lock some profits from time to time
Of course that this is very nice, but it also depends a lot on the availability of your money to buy crypto and to hold... never invest what you can't afford to miss