It is never a good thing to sell all your coins at once if you because there is always a chance that the price is going to still rise.
If you have then sold everything then you just missed out on some money.
Don't put all eggs in one basket, price can also get lower but if the amount of the bitcoin volume is low then the loss isn't much to care about because you risked that money and are able still to sell them so you don't lose 100%
Its always better to sell them in parts as future will allow you to make huge profits if price goes higher so selling everything is never recommended.
reading the OP this topic was about the stock market fall of early 2016 and i do believe that even if some of your investments (stocks or anything else that you included as a diversification) stayed up or even gone higher, but you shouldn't be greedy and sell it if you feel like a fall is incoming and the chances of losing money is getting high.
it is always better to miss out on profit rather than losing money because you held.
Exactly. This is from early 2016. There's always a dip in January / February but this one was bigger than 'normal' (Whatever that means). People did sell and the markets have since recovered. At this point things could go either way, but we seem to be out of the worst of it.