That's simply because cryptocurrencies are volatile, basically. Don't expect it to rise all the way up without having a day or time that it will fall down too. If 2017 is going to repeat again in the coming years, i am sure that i will have a better profit than what i have last 2017 because i have already invested well during this time.
it depends on how long you save your investment. if you need money before there is a market growth will you not sell it? it will be a difficult choice because everyone really looks forward to the 2017 market again but that seems to be difficult.