Well bubble were caused by the huge whales who are buying a large amount of stocks or commodities.
Just look at the housing bubble. That was caused by millions of ordinary people buying houses that they ultimately could not afford.
A bubble is caused by speculative buying by many small investors. It may be triggered by whales making large buys, but it isn't a bubble until it becomes mainstream.
We are not there yet, but it will be time to exit when you see waves of newbies talking about how much their bitcoin investments are worth.