"A knight on the rim is dim/grim” (or “knights on the rim are dim/grim") is a chess adage meaning that a knight on the edge of the chessboard has less mobility. Knights are more advantageously placed in the center of the chessboard.
“Knight on the rim is dim” has been cited in print since at least 1964. The author of the rhyme is unknown; the influential chess player and teacher Siegbert Tarrasch (1862-1934) is sometimes credited, but there is no evidence that he used the rhymed form.
Wikipedia: Knight (chess)
The knight (♘ ♞) is a piece in the game of chess, representing a knight (armoured cavalry). It is normally represented by a horse’s head and neck. Each player starts with two knights, which begin on the row closest to the player, one square from the corner. Expressed in algebraic notation, the white knights start on b1 and g1, while the black knights start on b8 and g8.
A knight should always be close to where the action is, meaning it is best used on areas of the board where the opponents pieces are clustered or close together. Pieces are generally more powerful if placed near the center of the board, but this is particularly true for a knight. A knight on the edge of the board attacks only three or four squares (depending on its exact location) and a knight in the corner only two. Moreover, it takes more moves for a decentralized knight to switch operation to the opposite side of the board than a decentralized bishop, rook, or queen. The mnemonic phrases “A knight on the rim is grim” or “A knight on the rim is dim” are often used in chess instruction and reflect these features.
But here a Knight on the rim is dim.
7 August 1966, New York (NY) Times, “Chess: The Piatigorsky Cup” by Al Horowitz, pg. 102:
“A knight on the rim is dim.”
17 July 1972, New York (NY) Times, “Fischer Turns Unorthodox Move Into an Attack” by Al Horowitz, pg. 25:
Rarely is a knight played on the rim as Fischer played it here and the remark “a knight on the rim is dim,” is often heard.
By Monroe Newborn
New York, NY: Academic Press
“Knight on the rim is dim,” ...
Playing Computer Chess:
Getting the most out of your game
By Al Lawrence and Lev Alburt
New York, NY: Sterling Pub. Co.
As the great Dr. Siegbert Tarrasch put it: “A Knight on the rim is dim!” Or as Tartakover said, “Some Knights don’t leap, they limp!” Make sure yours are in the bright sunshine and leaping. Keep them near the center!
Lubbock (TX) Avalanche-Journal
Polgar: The Viking phenom: 19-year-old Norwegian ranked No. 1 in world
Published: Sunday, December 13, 2009
Remember the old adage about “a knight on the rim is dim”? Notice that all three knights are on the edge of the board here. But Magnus’ knight is the least ‘dim’ of the three, though he wasn’t entirely happy to have it there.