If we have extra capital then we should invest in ETH for 10 years and it possible if we do it now this time market is bear and we can buy at low prices and we can hold for future so we can become the successful investor of this currency.
If investment in 10 years is a long time, it may be difficult for us, then ETH may not exist, so do not hold time too long, so it will be dangerous. For you, I think ETH can hold until 2019, if the past 2019 but their value does not rise, do not wait anymore.