People are "round" predictable creatures. People like round numbers. 20.000 $ is a very round number, once BTC hit 20.000 Sell! It's falling, OMG Selll moooore!

Let's see other "round numbers":

It passed 15 (17), fell to 13
Before that 11 and immediate 9
5 and 3.3 in two weeks
1.150 to 750 in one week
500 to 320 ...

Beware of Round!
And Beware of Holidays
Don't go to the gym on Monday, everybody are starting on Monday