The ever-present past

A moth once setttled, plump and brown, upon my coat
As drizzle in a garden fell so many years ago.
And when, as boy, I chanced to glance and saw her on my chest
Her silent presence brought strange fright that had not touched me as
Her dampened wings were folded when she fluttered down to rest.

Too hastily I brushed her off and saw, as she took flight,
What beauty I had banished by an unconsidered act.
Too soon she vanished midst the ranks of raspberry bushes thick.
Too late and vainly did I seek to catch a moment gone.
How silent was the air around while weightless droplets fell
Upon the dripping leaves through which the ripening berries peeped.

Why does this timeless memory stay with me to this day?
Why will it without doubt retain its  charm and potency?