What is last-mile delivery and why is it the most expensive leg?

Last-mile delivery is the final leg from local distribution centre to the customer's door. It accounts for up to 53% of total shipping cost because it involves individual stops, failed delivery attempts, and urban congestion. Failed first attempts add 1+ days and increase costs. Offering out-of-home delivery options (parcel lockers, pickup points) can reduce last-mile costs and improve success rates.