Sometimes when I talk about big things in the future, I don't really grasp them. It's not that I don't have the information about it - I knew, when I went to the Philippines last year, that on the way back I'd have one flight leaving 16 hours after my previous one arrived. I had all the information, I had the itinerary, I knew the gates, I had the map of the airport. But I hadn't accurately imagined what sitting in an airport for 16 hours would feel like... what it would be like to arrive outside the Manila airport and find a single line of chairs bolted to the concrete wall, full of people sleeping, with a line of people waiting for anyone to leave an unclaimed chair so they could take their turn. As much information as I actually had, I still hadn't really understood on a gut level what the situation would be.
I think it's a type of scope insensitivity:
Once upon a time, three groups of subjects were asked how much they would pay to save 2000 / 20000 / 200000 migrating birds from drowning in uncovered oil ponds. The groups respectively answered $80, $78, and $88It turns out that when you ask someone a question like this, they imagine one bird drowning in an oil pond, and then rather than actually do the multiplication, our brain kinda sorta imagines a bunch of them at once, and picks a number based on that. The actual number doesn't really matter, only that they're "big" numbers, because our brain does the same "kinda sorta multiply" operation for any number that qualifies as big.
I've noticed that the same thing happens with bit amounts of money, for example budget numbers from the government. A news article can list a government program and say it costs "X dollars," and as long as X contains one of "million," "billion," or "trillion" it will have essentially the exact same impact. Most of the (usually) outrage at how little/much is being spent will be drawn from context cues by the writer, not by the actual number.
The human brain just isn't equipped to deal with numbers that big on an intuitive level. And why should it be? In a hunter-gatherer tribe of 50 people, when would you ever experience 2,000 of something, let alone one trillion?
I think my brain does something similar when thinking about the future. In the context of a tribe of hunter-gatherers a few thousand years ago, just like our brains didn't need to handle large numbers , I don't see why they would need to handle specific, extended, future scenarios. Sure, it's necessary to think about the future so you can, fore example, plan for the winter and save up food. But you don't need to imagine every single time you set aside food for later simultaneously - life over a period of months was similar enough that you could just imagine it once, and then "kinda sorta multiply" it by "a bunch of days."
But with a trip like this one, or a trip like the one I took to the Philippines last year, every day is different. It's different traveling, it's different scenery, it's different plans, it's different sleeping arrangements... and it all has to be thought about. It's not like most desk jobs where you know you're going to work, and you don't have to plan specific work activities until you're actually there and working. It's not like a normal vacation where you can wake up in the hotel and plan out where you're going. It all has to be thought about at once - because where I'm staying depends on how far I travel which depends on the weather and how far I was able to make it the day before...
It's taxing to think about it all at once, and I don't think I ever did before. I imagined camping out one night, and sorta kinda multiplied it. Now that it's all laid out before me, it's a little more clear. As much as I talked about this trip before, I hadn't once imagined what it would actually mean. What I would actually be doing, day to day, night after night.
But I did it anyway. I kind of knew I hadn't been imagining it correctly, and said as much to a few people. And I knew that most likely, the parts I was imagining most incorrectly were also the parts that would be hardest - camping out, getting meals in areas without many people, etc. I knew that it would be hard, and that I wasn't imagining it correctly, and that it would be more unpleasant than what I imagined.
But here I am, doing it anyway. Parts of it will suck, and it will almost certainly be harder than I ever imagined, but hey - it'll make a good story, right?