A beard can dramatically alter the apparent shape of a face.
A particular haircut can change the proportions of someone's head.
Clothing can create another layer of visual similarity.
Douglas and Stirling happened to share several of these features at once: reddish hair, beards, similar facial characteristics, and a broadly similar appearance.
That combination made their resemblance particularly striking.
The Power of Context
There is another reason their resemblance may have seemed so extraordinary.
People do not judge faces in isolation.
We interpret faces within a larger visual context.
If two men have similar hair, similar beards, similar clothing, similar expressions, and are standing beside each other, the brain naturally emphasizes the similarities.
The effect can become stronger when someone has already been told that the two people look alike.
Once the idea is planted, the observer begins searching for matching features.
That does not mean the resemblance was imaginary.
The photographs clearly showed why people reacted so strongly.
But perception can amplify resemblance, particularly when two people are deliberately photographed side by side.
In Douglas and Stirling's case, the circumstances created almost the perfect setting for this effect.
They were seated next to one another.
They were dressed similarly enough to reinforce the impression.
They had comparable hair and beards.
And, most importantly, they were both smiling at the same time for the photograph.
The resulting image made the two strangers look almost like a carefully assembled pair.
The Internet Made the Coincidence Even Bigger
Before social media, a story like this might have remained a funny memory shared between friends.
Someone might have taken a photograph.
The men might have told their families.
A few passengers might have mentioned it later.
Then the story would probably have disappeared.
But in 2015, social media could transform a strange personal moment into an international story within hours.
That is exactly what happened.
The photograph circulated rapidly online, attracting thousands of reactions and eventually the attention of mainstream news organizations.
ABC News reported that media outlets began contacting Douglas after the photograph spread online.
The Guardian, CBS News, The Independent, the London Evening Standard and other outlets subsequently reported the encounter.
There is something particularly well suited to social media about the story.
It requires almost no explanation.
You can see the photograph and immediately understand the joke.
Two strangers.
Two almost identical faces.
One airplane seat.
Then the same hotel.
Then the same pub.
The story practically tells itself.
The Human Appeal of an Impossible-Looking Coincidence
Stories about coincidences have a special place in popular culture because they challenge our intuition about probability.
We understand intellectually that unlikely events can happen.
But when several unlikely events occur in sequence, the experience feels almost impossible.
Consider Douglas's journey.
He traveled to Ireland for work.
A stranger happened to be sitting in his assigned seat.
That stranger happened to look remarkably similar to him.
The two happened to be photographed together.
They happened to stay at the same hotel.
Then they happened to visit the same pub on the same evening.
None of these events individually violates the laws of probability.
Together, however, they produce a story that sounds almost fictional.
That is why people love coincidence stories.
They remind us that everyday life contains countless possibilities that we rarely notice.
Every day, millions of people travel.
Millions check into hotels.
Millions walk into pubs, restaurants, cafés and shops.
Most encounters are completely ordinary.
But occasionally, two unrelated paths intersect in a way that produces a story worth remembering.
Douglas and Stirling happened to experience one of those moments.
From Strangers to Drinking Companions
Perhaps the most charming part of the story is that neither man reacted negatively.
The situation could easily have been awkward.
Douglas could have become irritated when he discovered someone in his seat.
Stirling could have felt embarrassed about the seating mistake.