Is the job REALLY that bad?

I cannot figure out this whole "postal shooting" thing. Apparently, a former postal employee killed a bunch of people at a mail processing plant, then herself, this week. Another victim, her neighbor, has been found as well. So, what is it with these people?! Why do postal workers lose their shit and kill everyone?! What is so freaking stressful about that job that they need to start shooting people? I think it's been a while since a mail worker went looney, I was a kid when the term "go postal" was really popular. So, what gives? Why all the disgruntled employees? They get paid well (considering it's not a job that requires much education), get good benefits, and a hell of a pension plan... I just don't get it. My job is harder than that, and the pay fucking sucks. Any postal employees want to chime in on this?