For some people it takes a week; for others a few years. But everyone, at some point in their lives, will get sick of travelling.
Airports, which were once the fuel of such excitement and anticipation, become a waking nightmare. They're a pain to get to. They're expensive once you're there. The food's fantastic – as long as you like lukewarm Red Rooster.
The security queues just seem to get longer and longer; more and more painful. The pat-downs feel more intrusive. You become tired of the constant assertions that you're carrying a cigarette lighter.
(Although maybe that's just me – I've got a USB stick that apparently looks a lot like a lighter when it goes through an X-ray machine. The conversation goes like this: "Sir, you've got a cigarette lighter." "No, I don't." "Yes, you do." "No, I don't." Zip... "OK, you're fine.")
The flights seem to take longer. Crying babies seem to become more plentiful. Filling out immigration forms feels like being given homework at school. Do I have to?
You seem to be going through a never-ending cycle of unpacking and repacking your bag. And all your clothes are dirty anyway. You're tired of cold showers that dribble onto you from above.
Foreign languages aren't exciting anymore, they're frustrating. Those charming salespeople down at the local markets are now just trying to rip you off.
And what about business travellers? I don't know how you guys do it. People who travel endlessly for work, who have to go through all the crap of airports and train stations and bus trips but don't get the payoff of a fun holiday at the other end? I can see how you'd never want to leave home again.
As you might have guessed, I'm coming to the end of a fairly heavy period of travel. It's been amazing, don't get me wrong, but it's time for it to finish.
In the last two months I've been to seven countries over four continents. I've been through 11 airports while taking 18 flights, eaten about 32 airline meals, and had six bouts of jet-lag. I've mangled four different languages, had two mysterious illnesses.
I've stayed in 18 different homes, hostels and hotels. I've taken to pulling T-shirts out of my bag, sniffing them, thinking, "Eww...", and then putting them on anyway. I have unexplained bites on me from unidentified places. It's become normal to carry my own toilet paper.
And now, sitting on the final flight home to Australia as I write this, I'm sick of travelling.
I've seen some incredible things over the last eight weeks and met some great people, but at this point in time a home-cooked meal, my own couch and a reliably hot shower sound like the new wonders of the world.
This isn't the first time this has happened. I was sick of travelling after my gap year, and I was over it after spending seven months camping through Africa and Europe a few years back. It happens. You never want to see your backpack again.
But that feeling has never been permanent. Maybe some people get sick of travelling for life – I get plenty of emails from people saying they now prefer to travel vicariously through stories than by going through the hassles of the experience themselves.
That hasn't happened to me yet. I get back to Australia, I make a home-cooked meal, spend some quality time in a scalding-hot shower, sit on the couch for a day watching Fox Sports News and a few Simpsons marathons, and I'm back in business.
That usually takes a week or so. Which means I better start planning the next trip now.
Have you ever got to a point when you've been sick of travelling? What were the signs that it was time to go home?