Buirnt Norton, by T.S. Eliot is one of my favorite poems; it means so much and reflects what I've many times thought about. Here's a little portion of the first of four quartets:
Time present and time past
Are both perhaps present in time future,
And time future contained in time past.
If all time is eternally present
All time is unredeemable.
What might have been is an abstraction
Remaining a perpetual possibility
Only in a world of speculation.
What might have been and what has been
Point to one end, which is always present.
Footfalls echo in the memory
Down the passage which we did not take
Towards the door we never opened
Into the rose-garden. My words echoThus, in your mind.
But to what purpose
Disturbing the dust on a bowl of rose-leaves
I do not know.