Stress
As an elevator technician, your stress level should be in a fairly manageable range most of the time. This job is very proactive as opposed to reactive.
You don't sit around and wait for something to break, only to temporarily fix it. Instead, you monitor, you schedule, you study the mechanical wear and tear so you know exactly what to expect. Replace it before it breaks—that's your motto.
Of course, things will go wrong. You'll have your fair share of stuck elevators, filled with people afraid they'll be trapped in limbo forever. You may even have to shut down an elevator or bank of elevators if something goes really wrong. But due to your diligent monitoring and preventative care of those systems, such occurrences should be rare.
Sweat the small stuff so you won't have big stuff to sweat later on.