They aren't told. They are recommended to hold. Why? Firstly, because it's not going to zero, not now, not ever. Even if some governments ban it, it will still be embraced by others who want to show that government the finger.
Secondly, because it's not inflationary like fiat currencies. Its supply is limited, and it will still be there when weak fiat currencies are long gone. Read about the life expectancy of an average fiat currency. You'll be amazed how quickly they lose value and get replaced by new ones.
Why should we sell? I got my coins for cheap and although they've been through ups and downs their value is still higher than it was a year ago.