Because the result SOUTH, NORTH, WEST still has the opposite pole next to each other, i.e SOUTH, NORTH. It is also mentioned in the description towards the end. I hope this helps.

{"NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"}
According to the instructions, NORTH followed immediately by SOUTH cancels out, and vice versa. Same case for WEST and EAST.
Thus the nett result is SOUTH, NORTH, WEST.
Then why is the result expected just WEST?

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ooh.. i get it. it plays by tetris logic.