A common pattern is: people (I supposed I mean: investors) are somewhat worried that markets are over valued. They ponder, think, research, binge-watch Prof G videos... Then they travel to have Thanksgiving dinner with a bunch of in-laws. Market gets discussed over cigars. If they get a confirmation signal from the brother in law attorney or sister in law dentist that they are worried too...then after mulling it over on the flight back to Denver...the market dumps on Monday.