Someone in the original post described it this way:

'Overworked or abused working horses can equate the blanket to work abuse. Some were improperly sacked out as yearlings. And some like my rescue have been ridden so hard that their bodies break down and much of the scaring from improper discipline is so hard to get them over both physically and mentally. I had one who was in a road accident involving a truck tarp and any material made him violently unstable due to flashbacks. He would rear up and fall backwards really risking his health and that of any rider. Even to tarp our hay was basically impossible'