Opportunity

I got up out of bed last night to jot down this bit of doggerel:

OPPORTUNITY
This gentle caller only knocks—
He does not ring the bell—
Nor pelt the windowpane with rocks—
Nor toot a horn—nor yell—

He does not flash a signal-light—
Nor wave a semaphore—
And when he calls upon a night
Woe unto them who snore—