Meanwhile, halfway around the globe in an African country barely the size of Maryland, drone deliveries have already taken flight—with more serious cargo than burritos.

In October 2016, Rwandan crowds cheered the launch and landing of delivery drones developed and operated by Zipline, a San Francisco-based startup. The locals call the Zipline drones "sky ambulances" as they soar overhead and swoop in low to drop off lifesaving blood supplies by parachute to remote hospitals and clinics located hours outside the Rwandan capital of Kigali. That may sound very different from the PR circus surrounding Google drones testing delivery of Chipotle fare to Virginia Tech college students—and it is. But Zipline and similar delivery drone pioneers have also learned some valuable lessons about what a large-scale delivery drone operation can look like—and whether Silicon Valley can ever realize the dream of drone delivery to your doorstep.