Make the Common Case Fast

In making a design trade-off, favor the frequent case over the infrequent case.

This principle also applies when determining how to spend resources, since the impact on making some occurrence faster is higher if the occurrence is frequent.

Improving the frequent occurrence:

bullet Helps performance

bullet Is simpler and can be done faster

A fundamental law, called  Amdahl's Law ,can be used to quantify this principle. 

Compare different cases