To the two explanations of why go is hard for computers 1 many legal moves and 2 no eval function I think you should add 3 long game If a program is computing a variation tree it s not only the breadth that makes it difficult but the length Things like playing for good shape in the opening can t be evaluated by going through variations since their benefit will come 200 moves later in a fight or in having priveledge to a good endgame move