Do bubbles always pop or can they just be considered rapid growth that is sustainable?
No, serious question
The price moves between the upper and lower trend line. "Bubbles" are merely a move from the lower trend line to the upper. They tend to move quickly because enough people bought at the lower or good news, etc.
When it reaches the upper trend line there is nowhere to go but down...so people try to cash out before everyone else. It bounces back and forth between the two.
I believe this trend will end when the ETFs go public, then it will stabilize.