As a PSE, I've learned commitment and teamwork are essential attributes for growth and opportunity within or outside the USPS.
As for the work itself, it's rather easy, but the body has to deal with constant repetitious movements for the entire shift. However, in time, you'll become accustom to the work physically, as well as, mentally.
And, yes, the mental aspect is the toughest part of the job. The hours are sometimes long, especially during Peak Season (Holiday season). And you could work on Christmas Eve, Christmas Day, New Years Eve, and New Years Day. But the good news, the Union negotiated Holiday Pay on July of last year for PSEs, so you'll perk-up once you see your paycheck.
Finally, the work culture has its moments. But what job environment doesn't have a clash of personalities? This is where mental toughness comes in. Do you job and do it well, and go home.
Pay, benefits, and room for opportunity
Seniority-based and long hours (PSE)