Have you ever used a clothes line as a zip line?

No. My son and his buds made a zip line out of thick, braided wire and made me go on it. It broke. I chased them all around the yard trying to whip them with that 20 ft. length of braided wire. They just ran and ran and laughed and laughed.

No, I’m not a zipper

No, but now that I’ve read this, I will try it at home. ;)

The stresses on that rope and the mounting are many times the load placed in the center. You can estimate it by looking at the angle the rope makes with the horizon, call it theta, when a load L is placed in the center. The force F on the rope is estimated to be F= L / sin (theta).

If L is say 200 pounds and the rope is pulled tight enough so it is 5 degrees from the horizon when L is in the middle then the force could be estimated at 200 / sin (5 degrees) = 200 / 0.087 = 2400 pounds . This is a very rough estimate but it should give you the idea. A 550 pound rated parachord would immediately snap even though the load is supposedly only 200 pounds.
There are true calculators that figure out the load but this rule of thumb has worked for me.

My son and his buds didn’t do the math, obviously. Just threw that puppy up there!