A speaker asked the audience "what’s 3,549,752 divided by 23,234 ? Quickly, who has the answer?"
Everyone fell silent. Some people pulled out calculators to do the math, and finally someone yelled out the answer after a few seconds. Then the speaker asked the exact same question again. This time everyone was able to immediately call out the answer. This is a great demo of the concept. The initial time-consuming process was done once, then after that, when the same question was asked, the answer was readily available, and delivered much faster. Read more http://blog.wp-rocket.me/wordpress-page-caching-explained-in-plain-english/