A good view of how the angled poles with their guy wires hold up the hopyard.
I already told the story of my friend who nipped the corner wire with the tractor and the whole yard fell.
The same principle applies to the end posts of a row in the vineyard. That triangle of post, wire, and ground on each end of a row keeps the support wire tight and the posts in between vertical and stable. The row can be incredibly long--quarter mile? half mile? and as long as those end posts are secure in the triangle, the row is stable.
Did you realize there was that much geometry in agriculture?