Your aim: To fill a pickle jar to the absolute maximum. The things that you can put in: Water, Pebbles, Rocks and Sand.
The stupid way: Fill the jar with sand, put some rocks in, try to squeeze in some water and then add pebbles. The sorry jar will vomit out the things you throw in.
The intelligent way: Fill it with rocks, then the small pebbles, add some sand till you can’t squeeze anything in and then add water. It’ll take even more than you can throw at it.
The pickle jar theory of time management works in a similar vein: To efficiently use your time, assign tasks that takes the longest to complete first. Then smaller and smaller tasks until your time is filled. I like this method because of its simplicity and because of the pickle jar analogy.