It is easy to feel like you have to cite everything and that your reference sheet will end up longer than your paper. Fear not! There are some things you don't need to cite:
Examples: The tooth fairy is a mythological creature. Students use number 2 pencils when taking the SAT.
Reason: These are longstanding truths and understandings that are not attributed to a particular person.
Examples: Mary Tyler Moore was born December 29th, 1936. The bombing of Pearl Harbor took place December 7th, 1941.
Reason: While you could say at the end of your paper that Mary Tyler Moore showed her face in this world just a few days before the coming of 1937, would you really want to? Do you have to? The answer is no.
Example: I believe Bessie Darling's Halloween murder to be the first in a string of 1930s mountain crime.
Reason: This is the conclusion that you have made, all by yourself, from all your studious research.