It is a painful, intimate trial, more psychodrama than courtroom drama, more about the mind of a man than the assassination attempt on a president.

If the Von Bulow case was a family tragedy caricatured into a public soap opera, the John Hinckley Jr. case is a public drama refined into a family tragedy. This time the question isn't whether the defendant did it. The question is why he did it.

In the courtroom, they will argue the legal definition of sanity. The prosecution must portray Hinckley as an irresponsible, spoiled brat who "felt ordinary work was beneath him." The defense must portray him as a man obsessed with delusions, unable to control his own behavior.

But in a larger world, we know that something went wrong with John Hinckley Jr. We want to know what it was, how it happened. What goes wrong with people? What distorts the thing we call the human personality?

Before the trial, it was easy to speculate. We knew about the "country club" parents, about their oil money and their move from Dallas to Denver. We knew about an older brother and sister who seemed to do everything right.

We could note the physical similarities between Jodie Foster and Hinckley's mother as a young woman, draw the character similarities between Ronald Reagan and Hinckley's father, talk about the youngest son who just couldn't make it in an achieving family. We could form a glib psychohistory, wrap up a perverse human story in reasons, and stash it in some distant corner, far away from us, from our families, our children.

But then, one after another--as if in some sad procession of the dearly beloved and bereaved--mother, sister, brother and father took the stand. Instead of clearing the psychological path that led to the Washington Hilton, they made it seem more subtle and elusive and true.

They checked in with their own memories. They bore witness to John's tragedy and their own helplessness. They, too, tried to track how the son who had made his father laugh at 10, the brother who had been home-room president at 12, faded into the loner who "managed to remove myself from the world."

In the most poignant moment of the whole trial, the mother, JoAnn Hinckley, explained, "John just seemed to be going downhill, downhill, downhill, downhill, and becoming more withdrawn and more antisocial . . . and so down on himself. . . . We were just terribly worried about him; we didn't know what was wrong, but we knew something wasn't right."

In desperation, she finally followed the "plan" of a psychiatrist who had seen Hinckley only a dozen or so times, and against all her instincts drove the son--"who looked so bad and so sad and so absolutely in total despair"--to the airport for a final goodbye.

By the end of the testimony, she seemed so much like any parent, devastated by a child's disintegration, shaken by self-doubt, still trying to understand. Did they give the boy too much or too little, hug him too close or push him away? Did they seek a psychiatrist too late, or accept his opinions too easily? What if they had not moved to Denver? What if they had not put him on that plane? What if? What if?

Bertrand Russell once wrote, "Psycho- analysis has terrified educated parents with the fear of the harm they may unwittingly do their children." You could hear that fear in the courtroom. "I am the cause of John's tragedy," said the shattered father. Forcing John away was, he believes, "the greatest mistake of my life."

The trial hasn't explained John Hinckley Jr.'s distorted life. It has intensified the mystery. It hasn't answered the questions; it has increased them.

But in a particular way, the very confusion of this psychodrama became a reality. It offered all of us a refresher course on how inexact our understanding of a human life really is.

Like all peoples, we devise myths to help know ourselves and our world: myths of religion and psychiatry, of chemistry and culture. There is truth in them. Yet none finally, fully, explains how a person becomes.

None solves the mystery of how a single one of us with our own uniqueness engages in a family, an environment, to become a self. None finally solves the mystery of why one child grows up and another breaks down.

In the courtroom finally there will be a decision about guilt and innocence. But in real life there is only the pathetic echo of JoAnn Hinckley's simple wish: "We wanted John to be self-supporting, to be a happy child, to stand on his own feet."