For years after inception, Amazon shipped their corporate personnel out to the fulfillment centers during the holiday rush. Jeff Bezos and the entire C-level team would fly to Lexington, KY or other distant locations and work the line. There is a very deep-rooted understanding of the criticality of shipping, and how vital efficiency in shipping process is.
Amazon uses a Kaizen approach to business, especially in the fulfillment centers. They create task teams of mixed-level employees, everything from order pickers up, and take suggestions about how to improve. Even tiny improvements make a huge difference when you're dealing on the Amazon scale. For instance, one Kaizen team mapped out a different order-picking path that reduced the steps walked by almost 1/3. Amazon quantifies every improvement in time and dollars saved. (Obviously this was for an area where the order picking is done manually; a lot of FCs have electronic order picking too.)
On top of all this, part of the Kaizen approach is that any worker can call a stop to the line at any time if a defect is spotted. It's an extreme approach to quality control but it forces overall improvement because too many stops draws attention to a problem earlier in the line and gets it fixed.
Kaizen teams that make improvements are publicly recognized in front of the entire company, with representatives flown to Seattle for an award at the company all-hands meeting.