It is absolutely rational decision to invest in ETH because right now, the cost of investment is low and you might achieve an edge over those who invested high and the second reason is that the market for Bitcoin is on the rise and the price is stable as well. This will eventually affect the market for ETH as well and ETH will follow the trend as well so there are chances for ETH to cross $2000 value till December when the values of Bitcoin will be more than $20000.