We took in a pony several years ago that after only owning for a few months was found one morning with a broken leg , at his age and where it was , there was no hope.
The euthanasia went wrong because when the vet inserted the needle the pony flinched , well more like jumped and came down on the broken leg , the shot of pain and adrenalin made it not go so well. Very horrific experience that I wouldnt wish on anyone.

"Blessed are the flexible for they shall not get bent out of shape"
"You can discipline and Discourage or you can Discipline and Encourage"
"Gentle in what you do , But firm in how you do it"