Good point! The text could probably benefit from a further clarification. You should gain a benefit befitting the fictional premise of the roll, then decide what happens and reduce an appropriate resource - so if you choose the same resource, they would absolutely cancel out. It's closer to the changing spirit of the game if you win some and then lose some(thing else), though! It's up to you if you prefer your story to have a "nothing happens" state, but that doesn't propel the fiction forward.