Why are people so concerned about "leaving peacefully"?

[stupid little girl]

I want to leave peacefully because I'm not a masochist. I have a low pain tolerance and any methods that could be super painful are unattractive to me. I just want peace with my death.

 

[Superdeterminist]

The fear response is not to be underestimated. With enough pain or terror, you will most likely back out, as determined as you think you are before attempting.