Of course not. Always diversify.
Thats right. Problems may occur if we only do it for just one coin. A good trader never leave all in just one basket. Better to have something left outside of it rather than risking everything although the return will be higher, the lost could also be stronger with that high risk.
There is no telling when it could go down. No one really knows when it could happen.
I can remember the saying of the successful businessman Warren Buffet that "do not put all eggs in one basket" that's why it confirms to the statement of a good trader never invest in one currency. It's always good to have a buffer asset which you can use for other coins which will be use for trading altcoins to earn bitcoins, which you can do it with lot's of altcoins assets that is now pumping. The opportunity might give you reason to grow your profit and increase your bitcoin by the time all coins will rise it's value, then you can sell for a good price. You can choose not only one, but plenty of assets which you can decide to dump when it reached its acquired value.