9/11 set certain events in motion; the recent scenes from Afghanistan are a reminder that they are still in motion.

The shadow of 9/11 is already very long.

So long in fact that even all these years later, conspiracy theories still abound. And not just on the fringes of society, either. Seminal director Spike Lee had to revise his recently released movie about 9/11 to exclude some of the especially controversial aspects of 9/11 conspiracy theories.

9/11 wasn’t a big conspiracy for one simple reason: Human nature.

We aren’t great at keeping secrets.

It is rare that two people can keep a secret for 20 years, let alone the thousands of people who would have needed to keep quiet about their role in carrying out 9/11 all these years.

Someone would have cracked by now. Someone would have been careless. People bare their souls to spouses, then get divorced. People get terminal cancer and make death bed confessions. Secrets don’t keep.

The reason for the conspiracy theories is also human nature. It doesn’t have anything to do with the melting point of steel.

When something huge and terrible happens, human beings want something equally huge and terrible to blame. JFK couldn’t have been assassinated by one disaffected malcontent with a rifle; it had to be a vast conspiracy. 9/11 couldn’t have been perpetrated by 19 terrorists and a handful of their cohorts; with something of this magnitude, it feels wrong to have the answer be simple.

The banality of evil always surprises us. The monster isn’t lurking in a graveyard on Halloween, evil incarnate doesn’t have horns and a tail. It’s a jilted suitor suffering from psychopathy. It’s people who kill their loved ones for the insurance money. It’s a cold-blooded murderer getting their hands on some terrible new weapon, as on 9/11.

For 20 years, the evil act perpetrated on 9/11 has informed U.S. foreign policy, military and intelligence decisions. While there might never be a good 9/11 movie- with good reason- plenty of documentaries have since explored that tragic day.

There are enduring mysteries, like that of the Falling Man, whose identity remains unknown to this day and who has joined other obscure and tragic mystery figures like Tiananmen Square’s “Tank Man” and the JFK assassination’s “Babushka Lady”.

There is a great deal we do know, however, almost too much; Some of it almost too painful to bear. It wasn’t yet the live-streaming digital age of social media, perhaps mercifully, but technology in 2001 did allow passengers on some of the flights and people trapped inside the towers to call their loved ones to say goodbye.

The shadow of 9/11 forces us to imagine what it might be like to make such a call. Or receive one.

What if you’re not home? What if you are? How do you say goodbye? Do you hang up, or would you be brave enough, or hopeful enough, to listen through to the terrible end?

Recordings of communications with flight control also paint a heartbreakingly vivid picture.

We know “Bye, babe,” and “I love you,” and “I’ll always be with you,” and “Pray for us, pray for us,” and “Let’s roll” were some of their last words.

We know some recited the Lord’s Prayer and the 23rd Psalm before taking action against hijackers on Flight 93; we know others made the sign of the cross before they jumped to their deaths from the topmost floors of the twin towers to escape the burning building.

“We’re in a new type of war,” some unknown dispatcher can be heard concluding in the historical record above, putting into words what a whole nation was thinking: That couldn’t possibly have been an accident.

He was right: When the second plane hit, it changed the world forever.

“That was on purpose, that was no accident,” someone can be heard exclaiming in the above video.

“No,” the videographer answers grimly; “no accident.”

Across the country, and around the world, on-air newscasters were coming to the same conclusion live and in real time: “This seems to be on purpose.”

Not even professional news anchors could hide their shock and dismay: “This has to be deliberate.”

About that time, these immortal words were being spoken to then-President George W. Bush, who was reading to elementary school students in Sarasota, Florida: “A second plane has hit the second tower. America is under attack.”

Around the world, people held candlelight vigils, they gathered in churches and synagogs, in cathedrals and mosques to pray for the victims, the survivors and rescuers.

In the months after 9/11, Americans were encouraged to stop watching footage of the planes hitting and towers collapsing; to stop listening to recordings of the desperate calls and voicemails. News networks now dominated by clickbait actually asked viewers to turn the channel and get professional counseling instead.

It seems like such a long time ago, but we haven’t forgotten.

The 20 year anniversary of the deadliest terrorist attack in U.S. history and recent events in Afghanistan have brought the events of 9/11 back to vivid life. In leaving Afghanistan, we were forced to recall why we went there in the first place.

We are also reminded, and painfully, with the deaths of 13 U.S. military service members in a terrorist attack on the Kabul airport, that for all our years in Afghanistan, global terrorism remains as big a threat as ever.

Our conflict with the group of religious extremists who believe provoking the West into war will bring about a prophecy of Armageddon is far from over.

Americans are still trapped in Afghanistan, in spite of U.S. State Department and military assurances to the contrary there are credible reports that some aren’t being allowed to leave at this time.

The New York Times and the Washington Post have just broken the story of the recent U.S. drone strike which killed, not a terrorist en route to Kabul airport with canisters of explosive but an aid worker delivering containers of water. And his entire family including 7 children.

This isn’t a news flash to everyone: As soon as the strike occurred, similar reports on the ground immediately began circulating on social media, in the international press and everywhere except the U.S. mainstream media, which took weeks to catch up.

Episodes like this are what makes the Taliban so successful in Afghanistan. Add a public still smarting from being lied to for 20 years about U.S. military successes in Afghanistan and reeling from all the devastating images of desperate and terrified Afghanis, and the shadow of 9/11 grows longer still.

The 20-years of military and intelligence failures which followed, and which cumulated in the disastrous U.S. withdrawal from Afghanistan, have added a footnote to 9/11.

It was deadliest terrorist attack in U.S. history- so far.

(contributing writer, Brooke Bell)