I buy and hold only coins i believe in such as bitcoin monero dash golem litecoin all the other ones i invest and when i see 40% gain i sell right vaway.
other coins as it is written above - will eventually worth zero.
like in the .com companies boom - amazon Microsoft and very few others went sky high and remained there but many other companies first went up and then lost all their value - same thing will happen with the mass of the cryptocurrencies and only few will remain