Tuesday (March 7) will mark the 58th anniversary of that terrible day in Selma, Ala., when future congressman John Lewis, Rev. Hosea Williams, Bob Mants, Albert Turner and some 600 men and women protesting Jim Crow and calling for voting rights stepped onto the Edmund Pettus Bridge.

They were lined up in twos marching peacefully. Lewis, then 25, was wearing a backpack with two books, an orange, an apple and toothpaste and a toothbrush inside because he expected, like many of his fellow marchers, to be arrested despite the fact that they’d broken no laws and wanted nothing more than their rights as Americans.

They had no idea what was waiting.

But when they came to the bridge's peak, they looked down and saw a wall of Alabama State Troopers below led by Sheriff Jim Clark, his hatred as clear as the button he wore on his lapel that said “NEVER.” When the officers stepped forward ordering them to disperse, Williams stepped forward and asked for a moment so the marchers could pray, not just for themselves, but for their oppressors as well.

That’s when they attacked.

After the billy clubs and the tear gas, 17 marchers were hospitalized, including Lewis who suffered a skull fracture, and 50 others were injured as the world watched Bloody Sunday unfold.

But as we remember this horrific event, too often we forget that Bloody Sunday didn’t happen on its own. It wasn’t some isolated weekend of hope and violence.

We forget February 18, 1965 when state troopers ambushed protesters calling for the release of James Orange in Perry County, Ala. We forget how they waited in the dark and attacked the marchers. We forget how one trooper tracked down Jimmie Lee Jackson who’d fled the violence with his mother and grandfather. We forget how that trooper shot him down in cold blood.

We forget how that murder prompted leaders like James Bevel, Lewis and others to plan the 54-mile march from Selma to Montgomery where they would take their grievances directly to Gov. George Wallace’s door.

We forget how Wallace called the march a threat to public safety and the organizers outside instigators. We forget how he ordered the highway patrol to "use whatever measures are necessary” to stop it.

And we forget how, two days after “Bloody Sunday,” Dr. Martin Luther King Jr., led 2,500 marchers onto the Edmund Pettus Bridge for “Turnaround Tuesday.”

You see, it’s easy to look back with the perfect vision of hindsight and see the long line of history bending toward justice. But it didn’t bend by itself.

It’s easy to look at one dramatic event and believe that one moment changes hearts and minds like it does in the movies when the music swells and the leading man speaks out. But that’s not how it works.

The movies don’t show us the years of struggle and sacrifice. They don’t lay out the hours upon hours of walking door to door. They don’t remember the sheer terror of a young man in rural Alabama praying to God that no one saw him walking into the SNCC meeting because, if they did, he might never be seen again.

Bloody Sunday wasn’t just a weekend. Change doesn’t happen by accident. Justice never comes from nothing. It takes us…all of us…committing ourselves to making a dream come true.

Movies might forget that part, but we never can.

Antjuan Seawright is a Democratic political strategist, founder and CEO of Blueprint Strategy LLC, and a CBS News political contributor. Follow him on Twitter @antjuansea.