Think about it: On the first move, white has 20 possible moves, 2 moves from each of the 8 pawns, making 16 moves, and 2 moves from each of the 2 knights, making 4 moves. 16 + 4 = 20 moves. At the start of every game, white has 20 possible moves. However, none of these moves can reach the enemy king, and none of these moves can give check. Without check, there with not be checkmate.
If you're wonder, what black responds with doesn't matter whatsoever, because even if black completely opens up his own king in that move, that ends move 1 and you do not have another move to actually deliver the check/checkmate.
@Kyojuro_Rengoku123, what about not classic chess, like Blitz or Bullet?
Think about it: On the first move, white has 20 possible moves, 2 moves from each of the 8 pawns, making 16 moves, and 2 moves from each of the 2 knights, making 4 moves. 16 + 4 = 20 moves. At the start of every game, white has 20 possible moves. However, none of these moves can reach the enemy king, and none of these moves can give check. Without check, there with not be checkmate.
If you're wonder, what black responds with doesn't matter whatsoever, because even if black completely opens up his own king in that move, that ends move 1 and you do not have another move to actually deliver the check/checkmate.