Nearly 20 years ago, I learned that sometimes the cheapest and most humane way to address homelessness is remarkably simple: don’t let it happen.

In 2008, I became homeless prevention manager at Transition House, a family shelter in Santa Barbara, in a position funded by the Women’s Fund of Santa Barbara.

Before that, I had spent several years doing case management and street outreach with New Beginnings Counseling Center and WillBridge.

I knew what could happen after someone lost housing.

At Transition House, I got a chance to intervene before the fall.

I remember one Latino family. Both parents worked and normally paid their rent. Then medical bills arrived that they simply couldn’t absorb.

My program could provide up to $1,000 if we could establish that this one-time assistance would stabilize a family and that they could resume paying their rent afterward.

We helped them. They remained housed.

Think about the alternative.

Once someone becomes homeless, costs begin accumulating almost everywhere: shelters, outreach workers, case managers, ambulance rides, emergency rooms and hospitals.

Police and firefighters respond to crises. Public works crews clean encampments.

Studies of chronically homeless and other high-service-use populations routinely put these public costs in the tens of thousands of dollars per person annually. A report by the California State Auditor cites estimates of $30,000 to $50,000 per year.

A major Santa Clara County study found that its highest-cost persistently homeless residents averaged $83,000 annually.

And those figures count dollars. They don’t count suffering.

They don’t put a price on sleeping frightened outside, being assaulted, losing possessions, watching physical and mental health deteriorate, losing a job, separating a family, or experiencing the accumulated trauma of homelessness.

Now compare those costs with Santa Barbara County’s emerging homelessness-prevention effort.

Data from the county’s two-year prevention pilot, presented publicly to the county Board of Supervisors in August, showed that approximately 400 people had been served at a full cost of about $3,250 per person.

Of that number, 85% retained their housing, with 93% reportedly still housed a year later.

During the pilot, county Homeless Management Information System data also showed overall homelessness declining 9% and first-time homelessness decreasing 31%.

Those figures do not establish that the prevention program caused the declines, but the reduction in people entering homelessness is encouraging.

The basic idea is simple. Find people experiencing an imminent housing crisis who can remain housed with some help. Caseworkers problem-solve with them, mediate with landlords, negotiate payment plans and, when appropriate, provide one-time financial assistance.

It sounds almost embarrassingly commonsensical.

The organization doing this work is Good Samaritan Shelter, led by executive director Sylvia Barnard, who has spearheaded numerous homelessness initiatives throughout the county.

Alexis Nshamamba oversees the prevention program and has been a tireless advocate for shifting more attention upstream.

Longtime homelessness advocate Glenn Bacheller has helped shepherd the broader effort to build prevention into our countywide system.

I have known Bacheller since his years with Social Venture Partners Santa Barbara. In 2014, he helped organize the Homelessness Action Summit at UC Santa Barbara, bringing national leaders associated with Housing First and the 100,000 Homes Campaign into conversation with local providers and citizens.

Bacheller offers a striking way of understanding the economics: based on pilot results, he says Santa Barbara County can keep about 15 people on the cusp of homelessness housed for roughly the cost of serving one chronically homeless person for a year.

But if prevention makes so much sense, why has it taken so long to bring it to scale?

My old friend, Jeff Shaffer, who has spent years working with Santa Barbara’s unhoused population, gave me an unusually candid answer.

“I think I spent so many of my initial years responding to the crisis of those who were chronically homeless and dying on the streets,” he told me, “that I myself am guilty of not being smarter related to prevention in the first place.”

That gets at something important about how our institutions operate.

Imagine people continually falling over the edge of a cliff.

We become increasingly sophisticated at caring for them at the bottom. We send ambulances. We operate shelters. We hire outreach workers and case managers. We build databases, conduct assessments and create coordinated-entry systems.

Every one of those responses is necessary.

But we can become so preoccupied with helping the people who fell last week that we fail to notice the people falling today.

We need to look up.

Shaffer independently reached for the same metaphor: “Fix the fence on the top of the cliff, and you won’t need as many ambulances below.”

Homelessness prevention is that fence.

It will not eliminate homelessness. Some people need permanent supportive housing, behavioral-health treatment, long-term rental assistance and intensive services. We must continue investing in those programs.

But many people are one medical bill, car repair, missed paycheck or unexpected expense away from losing their housing.

Good Samaritan and its partners plan to expand the effort into a countywide prevention system, bringing additional nonprofit organizations into the work.

Private funding can help it grow faster and more flexibly, including providing assistance where public funding restrictions might prevent intervention.

I met a family like that at Transition House nearly 20 years ago. A relatively small amount of money at precisely the right moment prevented a much larger human crisis.

If you are housed today but fear you may soon lose that housing, don’t wait until you are sleeping outside. Call Good Samaritan Shelter’s Housing Problem Solving Hotline at 805.621.6882.

We will always need shelters, outreach workers, case managers, supportive housing and compassionate people helping those who have already fallen.

But Shaffer is right: “Fix the fence on the top of the cliff, and you won’t need as many ambulances below.”

Sometimes the most humane and least expensive way to end someone’s homelessness is to make sure it never begins.