Money.   A means of exchange, and a store of value.

As one, it oils the wheels of commerce, industry and everyday life.  Enabling us not just to transfer value between each other, but to generate new value for each other.

As the other, it locks up not just its current value, but also all the potential value it is able to create.

Too much oil in the system can be wasteful, but not enough is catastrophic.

Hoarding is counter-productive.  Money needs to move to be really useful, and the more parts it can reach, the more useful it will be.