There is no rule for that. It depends on your satisfying level. When your profit is $3 for 1 coin, you sastified, you can sell. But with otheres, they arenot. They still want to wait for higher profits.
That's all.
The decision of selling will come when you satisfy with the price at that time.
Yes there's no specific rule when it comes on selling and buying but we have this basic rule as a business minded person to sell your coin once the price is valuable to your coin and buy when the coin price is down. However this simple rule is applicable to everybody it's up to them if they would follow this basic principle.