Answer: The poem is using drastic metaphors as a way to compare the YESEES, the NOEES, and the THINKFORYOURSELFEES' behavior.
Step-by-step explanation:
Shel Silverstein is using drastic metaphors to imply that the YESEES and NOEES' extreme attitudes and actions led them to have bad consequences. The YESEES wore themselves down by agreeing to everything, the NOEES lost opportunities due to fright, meanwhile, the THINKFORYOURSELFEES, had a neutral position and found a balanced lifestyle.