Example: I bought a bitcoin in December 2017 that time price of a bitcoin was 18000 USD.
Now 17 July 2018 I want to sale my bitcoin (today price is 7700USD 17 July 2018).
What price will be applied to my transaction?
The price on which bought or the price which is the recent price of bitcoin?
Once you paid BTC for 18000USD it's means no profits until BTC reach and grow up more than 20K$

Otherwise just Hold them and Pray for it !