It’s less than two weeks until Christmas Day and if you haven’t watched Home Alone yet, then seriously, what are you doing?

Those of us who haven’t committed crimes have only just noticed why poor little Kevin McCallister was left behind in the first film, with a TikTok video by creator Ivan Mars shedding some light on the mystery.

For the very few that don’t know, the iconic first film follows Kevin, who was accidentally left home alone (duh), and forced to defend his home against burglars Marv and Harry who plan on breaking in while the McCallisters are on vacation.

While it may just be a film, many have questioned over the years how on earth Kevin’s parents could have possibly left their young son behind.

How did Kevin get left Home Alone? Credit: 20th Century Fox

The most obvious answer that comes to mind is that Kevin got in trouble the night before their flight to France and was sent to sleep in the loft by himself as punishment.

Then, in the middle of the night, a storm caused the power in the McCallister home to go out, resetting all of their alarm clocks.

When they got a knock on the door from the airport taxi service, the family scrambled to get their luggage, tickets, and passport together, Kevin’s mom Catherine asks her niece Heather to do a headcount of all the children.

Heather’s count goes wrong on account of two people.

Firstly, Kevin’s older brother Buzz, who tries to throw Heather off by shouting out random numbers.

And secondly, the McCallister’s neighbour Mitch Murphy, a young boy Kevin’s age who comes over to chat with the kids before they head off on their holiday. Only seeing the back of his head, Heather mistakenly counts him.

When it appears they have everyone, the family rush off to the airport and head to Paris.

But wait… wouldn’t the McCallisters have had a spare plane ticket when they checked in? Shouldn’t that have given them an inkling that Kevin was missing?

There really are a lot of questions and not a lot of answers.

Kevin has to defend his home from the Wet Bandits. Credit: 20th Century Studios

That’s where the less obvious detail comes in. A moment so fleeting that many Home Alone fans had never even noticed it before.

You see, the night before the flight, Kevin got in trouble because he got in a fight with Buzz for eating his cheese pizza. The argument resulted in a litre of milk being spilled all over the table, soaking the pizza boxes, the family, and most importantly, the plane tickets.

After Kevin’s dad Peter grabs some paper towels to dry up the mess, he accidentally throws away one of the plane tickets – which would explain why the McCallisters don’t notice Kevin is missing until they’re halfway to France.

While watching the classic 90s film this year, one viewer spotted the tiny detail for the first time, and couldn’t believe he had never noticed it before.

“I’ve seen Home Alone ~25 times and it wasn’t until this most recent time I realised the dad threw away a plane ticket when cleaning up spilled milk at the beginning,” they wrote.

“That’s why they never had an extra ticket.”