Well here, let me explain: if gold is a bubble someone comes up and says, gold is overvalued, here's x, y, z that explain why it's overvalued. That idea spreads, people stop buying and start selling, boom bubble popped.
With bitcoin though, I don't see a good way to say bitcoin "is overvalued, here's x, y, z that explain why it's overvalued." There's really no explanation for it's value at all, that's the aspect of bitcoin that resembles a currency.
There hasn't actually been a reason for gold's value since 1933, when FDR took the U.S. off the gold standard. And gold has exhibited similar bubble behavior as Bitcoin since, eg. the 1980 bubble when it went up 5x in a year and then crashed 50% the next year, or the 2005-2011 bubble where it went up 4x and crashed by 40% over the next couple years.
It really is as simple as other posters are saying: when there are more buyers than sellers, the price goes up, and when there are more sellers than buyers, the price goes down. The reason for there being more sellers than buyers could be as simple as people losing interest and moving onto the next shiny thing. You can't eat either gold or bitcoin, so in the absence of continued attention, there's natural selling pressure.
No, like GP said, all it takes is for some people to sell large amounts of BTC, and for other people to notice and panic. That's it. IMO you're really overthinking things.
I suppose you're trying to guess why those first sellers would sell? Seems like a pointless exercise. There could be any number of reasons. A mysterious authority figure convincing them that BTC is overvalued is just one (unlikely) possibility.
