A little clarification is needed for those who are not coin collectors. A "proof" coin, made for collectors, is manufactured using highly polished planchets and multiple strikes and is handled with care during the minting process. A "mint state" coin is from the standard production run and is banged, dumped, bagged and generally abused while in the posession of the Mint.

Therefore, to a collector, a proof coin is totally different from a mint state coin. An standard run coin graded MS-68 coin is one of unually high quality and is often, but not always, considered rare. A modern issue proof graded PF-68 coin is a dog and is often not worth collecting.