Sand Castles (early teens)

Why do we build sand castles in the sand,
Right on the waters’ band?
We know they’ll fall
Before they’er ever built up tall.
But always we try
Then foolishly cry
When fate is carried out
And the sand’s all washed about.
Just the same I ask
Why do we set about the task
Of hoping for things that never will be?
But as I look around I see
That we always must
Just trust.
In things we know
never will come true.
I guess it helps us go
And gives our hearts something to do.