Mechanical sympathy is when you use a tool or system with an understanding of how it operates best.
You don't have to be an engineer to be be a racing driver, but you do have to have
Mechanical Sympathy. Jackie Stewart, racing driver
When you understand how a system is designed to be used, you can align with the design to gain optimal performance. For example, if you know that a certain type of memory is more efficient when addresses are multiples of a factor, you can optimize your performance by using data structure alignment.