[wtallis]

The why does come into play, often quite unexpectedly if you don't really understand how your memory system works. I've seen StackOverflow questions about performance anomalies that could only be properly answered by digging into the details of not just cache line size, but also cache associativity.

Not understanding how the system works means that sometimes you'll have to settle for not being able to use the full performance of your hardware, and that your performance constraints will in practice be rather inscrutable and often unpredictable.