Norvig's Law
Any technology that surpasses 50% penetration will never double again.
A somewhat tongue-in-cheek truism about technological adoption and numeracy in popular press. In point of fact, Norvig’s Law can be thought of as a maxim to apply careful thought to any discussion of numbers, and to define terms precisely. As Norvig himself points out, it is in fact possible to sell twice as more units by changing the metrics by which market penetration are measured - e.g. selling to individuals instead of households.