from Don't Let Me Be Lonely: “A father tells his son the thing he regrets most about his life...”

A father tells his son the thing he regrets most about his life is the amount of time he has spent worrying about it.
Worry 1. A dog’ s action of biting and shaking an animal so as to injure or kill it, spec., a hound’ s worrying of its quarry; an instance of this. 2. A state or feeling of mental unease or anxiety regarding or arising from one’ s cares or responsibilities, uncertainty about the future, fear of failure, etc.; anxious concern, anxiety. Also, an instance or cause of this.

It achieved nothing, all his worrying. Things worked out or they didn’ t work out and now here he was, an old man, an old man who each year of his life bit or shook doubt as if to injure if not to kill, an old man with a good-looking son who resembles his deceased mother. It is uncanny how she rests there, as plain as day, in their boy's face.
Worry 8. Cause mental distress or agitation to (a person, oneself); make anxious and ill at ease. 9. Give way to anxiety, unease, or disquietude: allow one’ s mind to dwell on difficulties or troubles.

He waits for his father’ s death. His father has been taken off the ventilator and clearly will not be able to breathe for himself much longer. Earlier in the day the nurse mentioned something about an electroencephalogram (EEG), which measures brain waves in the cerebral hemispheres, the parts of the brain that deal with speech and memory. But his brain stem is damaged; it seems now the test will not be necessary. The son expects an almost silent, hollow gasp to come from the old man’ s open mouth. Those final sounds, however, are nothing like the wind moving through the vacancy of a mind. The release is jerky and convulsive. There is never the rasp or the choke the son expects, though one meaning of worry is to be choked on, to choke on.