It is still difficult to predict how much bitcoin price will reach in December 2019 because we cannot see what will happen in the future. We could only draw a line and predict what will happen later. Besides that, we don't have to be panic if somehow bitcoin price is down or up because if we decide to buy bitcoin and hold it for a long time, we will wait until the time comes to sell the bitcoin in the price we want.
predicting and seeing is a two different things and we should not joined them as if there are the same things. If we see were the price will be we would not predict but since we can not see were it will be that is why we predict or forecast. I am predicting bitcoin to be around $25,000 by December end 2019.