Throw a rock in a pond and you create a hole in water. Ripples abound, the edges get wet, calm destroyed.
And then it settles. The water fills the hole and the surface becomes still again. But the volume of the water is increased by the volume of the rock.
When someone joins an organisation, they’re dropped into the pond, they cause ripples, normality is restored. They’ve added to the organisation though, even if you can’t see them any more.