Watching “The Soloist” last night, I could not fight back the tears.

It is a film faithfully drawn from the memoir of Steve Lopez, a Los Angeles Times columnist who writes about and ultimately befriends a musically talented, homeless mentally ill man living on the chaotic streets of Los Angeles. The film is poignant and moving in a gritty sort of way. There is no sugarcoating here.

Early in the film, as Lopez sits in a plaza on a busy city street worrying about where his next column will come from, he hears the sweet and unlikely strains of a violin. He goes in search of its source and finds a homeless man beneath a statue of Mozart coaxing a lovely concerto out of a two-stringed violin. It is apparent that the man is both talented and well-schooled. Lopez has found his column.

At first Nathaniel Anthony Ayers is no more than a column to Lopez. Ultimately, though, Lopez becomes caught up in Nathaniel’s life as he attempts to improve it. He is both moved and frustrated by this bizarre but intelligent, educated man who resists his efforts to help.

I became involved in the movie, I suspect, more than most. I was Steve Lopez. I have listened to Nathaniel Ayers speak his gibberish. Like Steve, I have wanted — expected — have been certain I could fix Nathaniel. It would just take help at a shelter. It would only take an apartment — a home of his own. It would just take a psychiatrist giving him the right medicine.

Like Steve, I have been severely frustrated, angry even, that my efforts to help were rejected. Why? Why couldn’t Nathaniel see what accepting treatment and having his own apartment would mean to him? He could be comfortable and safe from the filth, drugs and crime on the streets. He might be normal and do the things normal people do. He might revive his extraordinary musical talent and make a successful — even brilliant — career of it.

Like Steve, I have felt guilty that I haven’t done enough, that maybe I don’t care enough.

But for me it’s personal. The mentally ill person I care about is my sister. She suffers from unrelenting schizoaffective disorder and, as with many of the severely and persistently mentally ill, medication is only partially effective.

My sister was a sweet, lovely child with intelligence, sparkle and wit. We were very close growing up, and I have many happy memories of swimming, playing tennis and sledding on the neighborhood hill together.

Like Nathaniel, she showed great promise as a young adult, obtaining a master’s degree in speech pathology and working in the field. She had her first psychotic breakdown at 26 — and ultimately became profoundly disabled. Losing her to schizophrenia felt like a death.

Last summer my sister came within a hair’s breadth of being — like Nathaniel — homeless.

After several years of stability her condition and her behavior deteriorated markedly, somehow escaping the notice of her case manager. By the time Connie’s medication was changed, it was too late. She was kicked out of the group home where she had lived for 10 years.

Connie’s case manager told me that her only alternative was the Women’s Shelter. As Connie put it, “That’s no place for a nice girl!” Indeed, as the shelter is open only from 6 p.m. to 6 a.m., Connie would effectively have been put out on the streets. As a “nice girl,” she’d have never survived.

I caught the next plane to Nashville and met with her mental health-care providers, who bent over backward to help. They found a new group home and fast-tracked Connie to an intensive treatment team.

I am happy to say that my sister has been steadily improving under the care of her new group home owner — an extraordinary woman who treats her boarders with respect, compassion and firmness. Connie seems happy — perhaps more so than she’s been in a long time.

Although it is tempting to relax and believe that things will stay this way, I know better. Anything can change at any moment and throw everything into turmoil again. I may have succeeded this time, but the next time she could refuse my help as she has before.

In “The Soloist,” Nathaniel’s mental-health worker tells Steve that the most effective thing he can do is to simply be Nathaniel’s friend. No living quarters, no music lessons, no medicine you can make him take, nothing is as stabilizing, meaningful or powerful as simply being there. Indeed, it is the only thing that works.

Steve feels he’s failed Nathaniel. But in the end he achieves a kind of peace when he realizes his friendship is enough. I suspect that Steve, like me, continues to find that peace fleeting, alternating with frustrating setbacks, unproductive efforts to fix things once again — and once again realizing that he can’t fix it; he can only be a friend.