Imagine having one bitcoin.
You sell that bitcoin at the current price(around 3800 USD).
Bitcoin crashes again somewhere around Christmass and the price goes down to 1K USD.
You buy 3.8 bitcoins with the dollars you got from the previous sale and you HODL.
In 2019-2020 bitcoin recovers to 10K USD (or maybe reaches 20K ATH).
You have made atleast 38K USD.

I know it's not guaranteed to happen,but hey,this is the Speculation forum,so why not speculate about this.
I think that this is every crypto whale's trading plan for the next 2 years.
Easy saying but very difficult to achieved that. I don't bitcoin will get to $20,000 in 2019 and it might not get to $1000 this year. Believe me that it will be difficult for you to buy bitcoin at $1,000 as you will be afraid that bitcoin is going to fall further. The best time to buy is now and not selling to buy low as you might be out of the equation.