If something is the scarcest, there is less of it than anything else.
The word scarcest makes people think of something very hard to find or get.
Examples:
Gold is the scarcest metal.
The scarcest animal in the forest is the panda.
Water is the scarcest thing in the desert.
The scarcest toy at the store was sold out in one minute.
The scarcest food in the world is the truffle mushroom.
The scarcest thing in the game was the magic sword.