Nylon and Steel have exactly the same resistance to breaking under tension. Explain then why someone would use a steel cable instead of a nylon cable for lifting a heavy load.
Nylon stretches much more than steel because it has a much lower elastic modulus. In the process of stretching to close to its maximum (ultimate) strength, Nylon will exceed its yield strength, and acquire a permanent deformation. After repeated use at close to the ultimate strength, it will break.
Lifting material with a cable that stretches a lot will make it diffcult to handle the lifted material, because it will vibrate up and down, possibly leading to damage.