Why do we say 'poker face' and other popular expressions

The origin of the expression “poker face” can be traced back to the second half of the 19th century Naturally, it came from the game of poker,

The phrase is used to signify the ability to keep a calm and composed demeanor, showing no visible signs of one's thoughts, feelings, or intentions Example

what are lottery numbers for tonight What does the noun poker face mean? There is one meaning in OED's entry for the noun poker face See 'Meaning & use' for definition, usage, and quotation

what hand beats what in poker I mean nothing, other than that adding a manual to the is “technically possible ” Herr Hofstetter has an excellent poker face, however