19 october 2016: 638,64$
19 october 2017: 5636,42$
It's about +900% in one year.
You're laughing for a +350% in 3 years. Why?

That is a great computation, and a good possibility to get that increase in less than 2 years.
Yes, this prediction is a little on the high side. I would be pleasantly surprised if we reached 20k that soon but I suppose it is theoretically possible based in this year's upward trend. It just seems unlikely that such a fast upward trend would continue for two more years without leveling off some, at least in percentage terms.
And with more and more speculation and predictions being released about bitcoins price in the next years. More and more people would consider investing on it that would result on getting a higher demand and faster increase on prices.
This is actually true the bitcoin value depeends on people and their interest only.the more people know about over the year millionaire story the more they will want to become one and start to invest in it.
more invest means more buy more buy means more hold and and more hold means price will shoot up in exponential rate.
I already seeing bitcoin in 100000usd..