Prices go up because money flows in.
In a bubble (up to you to decide if this is a bubble) a lot of people end up very wealthy on paper, but they only keep what they manage to sell before the retraction. Sadly, a lot of people can't resist the urge to double down as prices get higher and higher, meaning they lose more on the way down than they thought they were risking on the way up.
> Like somebody who put in 50% of their net worth today, and maybe it drops?
YOLOing your net worth into stocks isn't something that happens in the real world very often, contrary to what you see on WSB. The only people doing that either have severe gambling problems, or small enough net worth that they feel like they don't really care if they lose it all because they can start over.
The weird thing about this bubble is everyone he gets rich on extreme gambles seems to want to post it for internet cred. Makes it look like everyone's doing it.