Do you need to cite facts?

If the fact is well-known throughout the world (like, for example, that people need air to breathe is a fact that is well-known throughout the world), meaning almost everybody knows it, then it is not necessary to cite the source. BUT, if the fact was found/created by somebody else [and was published] (for example, "During my experiment, I learned that......" stated and published by Dr. whoknows, it would be necessary to cite that if you use that direct quote/information/etc. in your paper/etc. (like/as a citation), it would be necessary to site the person who said the quote (as directed and correctly for a works-cited page format) in your works-cited page, or whatever you call it (a page that cites, ect....). Hope this helps.