Each Being that enters this plane of existence is issued, among other things, a handful of sand. The idea is to use, expend, give away, the last grain of sand at the moment of passing into the next plane. Here is how it works:
A very young Being is more often the recipient of sand, from its parents, relatives, siblings, caregivers and is thus careless about letting sand slip through its fingers. As a Being progresses, it will start to give sand more purposefully: a grain to the playground, a grain to school, a grain or two (or five or more in the case of my son) to video games. The more mature Being then gives sand to a job, employment, career, trade, profession, avocation; and to other Beings. Soon there are a circle of other Beings receiving your sand and from whom you receive it back; but one, or two, or three, special, particular Beings who receive a lot of it. As a Being comes closer to passing into the next plane, they see that the once abundant handful of sand has dwindled to fewer and fewer grains and they become even more particular about giving them away. Perhaps some of the sand perviously given to a job is now given to golf or gardening or a new sailboat. [note:if the sailboat, prepare to devote a LARGE amount of sand. I'm just saying.]
As we Beings progress, we become more conscious of the passing away of our sand, and more careful where we bestow it. Sometimes we continue to give sand to another Being who does not value it. They do not give us sand in return, or they let our sand slip through their fingers onto the ground. Other Beings try to push more of their sand on us, perhaps trying to elicit an exchange, perhaps to garner sympathy, perhaps to put us in their debt.
The very best situation that can occur between two Beings is when sand is exchanged freely and given away joyfully. Then there is Love. Which is a whole 'nother story entirely.