If you're looking at a bit like an investment object , then surely everyone would like to that the rise will be steady and slowly. In this way, this market would be able to go up and down without any fear to increase their savings.
One thing with a huge spike in growth and most especially those that happen as a result of manipulations and greed, they can never be sustainable. It is a normal occurrence in any market and the market will always have to pass through stages, and trying to jump start it into becoming what it should not in a short term, the chances of seeing it retrace will always be there.
It is just like in normal life, you can force a child to grow quickly as there would always be a lot of things to learn along the line and if you take a child that is meant to be in basic school to a high school, his brain will not be able to sustain what is being taught. Just put that child in the case of bitcoin here.
So far, I can even say it is apparent that the market is always sustainable when there is a steady growth.
Nobody will consider quick growth as permanent because quick growth is always for short time and may be temporarily created. Slow and steady growth is always natural and according to the market cap. When the price increases with the market cap it will never drop in the future, but without investment the growth in the price is like the bump in the previous year. This thing is understandable.