When something "looks good on paper", it means that it makes reasonable sense when you think about it, but that it doesn't take into account one or more subtle facts which change the whole thing. A football play might look good on the chalkboard spelt out in Xs and Os, but it doesn't take into account things like the relative sizes and speed of opposing players, endurance, or desire to win at the moment the play is run.
I think it was Moltke the Elder who wrote that no plan survives contact with the enemy. This is a similar phenomenon.
I think it was Moltke the Elder who wrote that no plan survives contact with the enemy. This is a similar phenomenon.
