More Effective C++ 16: Remember the 80-20 rule
The 80-20 rule states that 80 percent of a program's resources are used by 20 percent of the code.
So when tuning the performance of a program, it's important to identify the 20 percent of code that really counts. And the way to do this is to use a profiler. A profiler can tell you which part of your program is using up most of the resources.