Corner is gold, edge is silver, center is grass
Corner is gold, side is silver, center is grass (金角银边草肚皮 jīn jiǎo yín biān cǎo dùpí) is a Chinese Go proverb. It means that territory in the corner is the easiest to surround, followed by the edge, and the center is the hardest place to get territory. Note that in this proverb, the center of the board is referred to as a belly (肚皮), so the literal translation for the third item is grass belly, or belly is grass.
There exist various "proverbs" to a similar end, such as "There is no territory in the center", "The center is just dame", that overstate the case and elicit responses by fans of Takemiya Masaki and other notable centre-oriented players.
See also: Corners, then sides, then center