Answer:
Its days are numbered.
Seven brothers, five work all day, The other two, just play or pray.
Sally, Lisa, and Bernadette are triplets. But Sally and Lisa share something that Bernandette does not. What is it?
What is used by man, tossed by trees, everywhere but unseen?
What goes trough your head but you forget it like 3 days after?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.