Seven years ago today my son, Aidan, died.  He was fourteen and his short and limited life continues to have profound effects on me, my family and people who have encountered him.  A piece I wrote on the second anniversary of his passing tried to capture his presence:

We had to
catch ourselves from characterizing him in terms of what he could not do, that
list was so long. He could not stand, he
could not walk, he could not see, he could not speak… But we came to understand the many things he
could do through his mere presence. He
could define our love. He could change
our vision.  He could inspire people
around him to demonstrate their humanity.  And he could make his father stronger.

He did make me stronger, in various ways.  And I strive to hold on to that strength in his absence.

The Daodejing helps me in this regard, by reminding me of the utility of absence, its tangible effects.  Here's passage 11 (Hinton):

Thirty spokes gathered at each hub:
absence makes the cart work.
A storage jar fashioned our of clay:
absence makes the jar work.
Door and windows cut in a house:
absence makes the house work.

Presence give things their value,
but absence makes them work.

The apparent emptiness is productive, it provides the essential complement to presence, without it existence would wither.

That is Aidan's continuing effect: he not only generates meaning in my life; he, in his absence, defines my presence.