Not all coins will have a strong future. There are even many suggestions that a large percentage of coins will actually fail. This can be due to lack of funding, lack of adoption, direct loss to competitors, and scam coins amongst others. Therefore pick the coins to hold using good research, as there is no point in holding coins that have weak ideas or are focused on providing a solution in a saturated area with superior peers. Such coins should be sold, and profit taken, before the inevitable happens and the coins are worthless