Rocks are big things that take up most of our time.
Sands are tons of trifles require moderate time.
Water are the rest of time that flies by quickly.
Keep in mind, Life is short and precious. We want to absorb as much as possible in our limited time span. Some people may start off with the sands and later on find out the rocks no longer fit in anymore. Some people just choose water but feel their bottle much lighter than others.
So, here is how we should do it:
Put in the big rocks first, then pour in the sands,shake it and lastly let the water flow in to fill up the space.
It is called prioritization in order to maximize value/time ratio or in another word to make the most out of our life.
This is a story my kindly mother try to tell me last night. Thank you Mom. =)