This is pretty much what I wanted to say. What is a surprising move varies greatly from player to machine. Here's a good example: http://www.chessgames.com/pe

This is pretty much what I wanted to say. What is a surprising move varies greatly from player to machine. Here's a good example: http://www.chessgames.com/perl/chessgame?gid=1064780 http://www.chessgames.com/perl/chessgame?gid=1064780 Capa's move 10 here (Bd7) is completely surprising to the vast majority of players and computers. It breaks most of the standard 'rules' of development and space control. However, it doesn't move the needle in terms of tactical significance at all. To me, that's a surprising move.