Your idea is correct. If the previou rate of return - as achieved in 2017 so far - is made in perpetuity, it takes as long to go from $10t to $20t, as it does from $5t to $10t. The $10 million price in 2020 won’t be achied unless the $ is falling fast or becomes worhthless Zimbabwe style.

There is no shortage of people who think that is likely, but there are more who think it will just carry on.

With less than 1 in 800 adults owning any bitcoin, there is plenty of room to maintain the price growth. When 90% of the population own bitcoin it won’t be able to grow at the same pace. I think we are good for a year or so, then the pace of growth will slow. Along the way we will have our 30%, 50% or 70% crashes which will shake out doubters.