Why is partial suspension so prone to failure?

[qualityOV3Rquantity]

i've seen many people here say it isn't an effective method and is likely to result in failure? why is this?

 

[PetrichorBirth]

Missing the carotid artery. Instead of blocking the carotid they block the jugular, and feel strangulation/pain/feel their head filling with blood instead of just passing out. So they stop after a while and declare it a failure.

Another big one must be stability of the objects you've attached the ligature/rope to. Your body will start spasming. In full suspension that's okay, because if the object can hold your weight you can move around all you want. But with partial suspension there's the risk of knocking stuff over, accidentally releasing yourself from the ligature etc depending on how you do it.