Did my vote make a difference?

So the ANC got 65,9% of the vote. That means they missed a two-thirds majority by 0,7%. About 20m South Africans voted. That means the ANC missed a two-thirds majority by 140 000 votes. South Africa had almost 20 000 voting stations.

That means, on average, it took only 7 votes per voting station to deny the ANC a two-thirds majority.

Now tell me it is not worth voting because, "What difference can one vote make?"