Selling your bitcoins is a matter of choice you can decide to sell it when and how ever you want,it's your choice,so what ever decision one makes concerning buying or selling of bitcoin is up to them.
You can't say that you have the profit if you won't sell. Selling your bitcoin isn't a stupid thing but we all need to do that in different occasions. The decision of selling only comes in few forms and I'll list them.
1. When the holder can't take the losses anymore.
2. If the holder listens to the FUDs
3. Holder sells if he needs cash.
1 and 2 are related to each other. When the holder are always listening to FUD and he's looking to his portfolio most of the time, he'll ending up can't take the losses anymore. I won't judge his act because before I did it but now luckily, I've learned from it.