Here are the adoption curves for a handful of major technologies in the United States. There are big differences in the speeds at which these technologies were absorbed. Landline telephones took about 86 years to hit 80% adoption.Flush toilets took 96 years to hit 80% adoption.Refrigerators took about 25 years.Microwaves took 17 years.Smartphones took just 12 years.Why these wide differences in adoption speed? Conformability with existing infrastructure. Flush toilets required the build-out of water and sewage utility systems. They also meant adding a new room to the house—the bathroom—and running new water and sewage lines underneath and throughout the house. That’s a lot of systems to line up. By contrast, refrigerators replaced iceboxes, and could fit into existing kitchens without much work. Microwaves could sit on a countertop. Smartphones could slip into your pocket.