Extended Metaphor

My brain is a raindrop on dead leaf.
It provides no nourishment, and it's useless.
Dripping down its shaft in September,
my brain is now unwinding
guided by gravity as it heads to its inevitable absorption
where it will remain in grounds of the school classroom
trying to grow a tree.
And when its leaves wilt in early summer
without sufficient water,
my brain will go through evaporation
and rain down in June
on another dead leaf.