Selling everything can be good, but it also depends on the point if you think you will make more profit in the future, I would not do it.
I even think because of the halving the bitcoin will go to a much higher amount, after the halving has been done they people will sell of course and than its the point to sell them on the best moment to make a lot of profit.
Selling everything would only be a good thing if the investment was completely compromised. Most of the time, there are chances that the investment can recover its value. I think the percentage of assets to be sold should depend on the chances that this investment has to recover.
That is true. For the bitcoin, it is better to buy and hold.