Why do we get stuck with a word after saying it a lot for a day, such as bro he's cracked, or big pot, or, indeed, or buster, and or, and etc.?

The major difference between the communist party in china and political parties in the united states is that a. in the united states, political parties have no role in government. b. in china, the communist party shares power with the national people's congress. c. in the united states, political parties hold widely differing views on almost every topic. d. in china, the communist party runs the government with no opposition.