I was on a platform at ten past six in the morning with two options on the board. One took a bit over two hours. The other took most of the day. I took the long one, and I want to be clear that I did not take it for a reason. I took it because at some point I had decided I was a person who takes the long one, and the decision had stopped being a decision.
I got in around half past five in the afternoon, having looked at a great deal of countryside through a window I could not open, and I was too flattened to do anything except find a bed and lie on it. The next morning I had one full day in a place I had wanted to see for two years, instead of the day and a half I could have had. That is an accounting error, and it was mine.
The slow option is not free
The way people talk about this, the fast train costs money and the slow train costs time, and time is the thing you have on your side if you are not in a hurry. That is not the whole ledger. The slow train also costs food, because you eat badly on it. It costs the ability to think, because six hours of sitting upright leaves you dull. It sometimes costs more money than the fast one, once you count the meal you buy out of boredom and the extra night you need because you arrived too late to do anything.
Most of all it costs the evening at the other end, and the evening at the other end is often where the good part of a trip lives. I have paid that price cheerfully many times. I just want to stop pretending it is not a price.
Fast is right when the trip has a spine
Some trips are built around one thing. A person you are going to see. A valley you want three days in. Something that happens on a particular morning. When a trip has a spine like that, everything else is access, and access should be efficient.
I get this wrong in a specific way: I treat the getting there as if it deserved equal billing, then arrive with a third of my energy spent and give the actual point of the trip whatever is left. If there is one thing at the centre, take the fast train, arrive early enough to be a functioning person, and spend the saved hours where the trip is actually happening.
Fast is right when the corridor gives you nothing
Not every slow route rewards you. Some corridors are four hours of retail sheds, motorway barrier and dark. A slow bus down a main road at night is not a route, it is a waiting room that moves. There is nothing out of the window because there is no window worth having, and the fact that it took longer does not convert into anything.
I have started checking, roughly, what the slow version will actually put in front of me. If the honest answer is a road I have seen a hundred versions of, I take the fast one and stop congratulating myself.
Fast is right when you are already worn out
Tiredness compounds. If I start a travel day already short of sleep, the long option does not gently unfold in front of me. I sleep through the good part, wake up with a stiff neck, miss the connection I meant to make, and arrive worse than I would have from a bad night alone.
The test I use is simple and slightly embarrassing: can I read? If I cannot hold a page for ten minutes on the platform, I am not in a state to receive six hours of scenery, and I should buy the shorter journey and treat it as medicine.
What the fast train does take from you
In fairness, it takes something real. On a fast line the country between two places becomes a rumour. You end up with a mental map made of dots and no lines, which is how people come to believe two towns are near each other because the trip is short, when there is a whole ridge in between they never registered.
You also lose the small transactions: the man selling something at a rural stop, the fifteen minutes on a platform where you can see how the town is laid out. Those are not nothing. They are just not always worth six hours.
Two things, and they take about a minute. Does the slow version run in daylight for most of its length, and does it go through the middle of places rather than round the back of them. If both are yes, the extra hours will probably put something in front of me. If either is no, I am paying for a chair.
The second check is about the far end. If I arrive late and everything I want is only available in the morning, the slow route has quietly cost me a whole extra day and I should price it that way.
The split I use now
Fast on the long legs, slow on the short ones. If the distance is big enough that the slow version eats a whole day, I buy the fast ticket and take a two hour local somewhere else instead, where the same amount of slowness buys me more.
The other version, when the trip allows it: fast out, slow back. Get there with energy intact, do the thing properly, then take the long way home when there is nothing waiting at the other end and being tired costs nothing. That one has worked almost every time I have used it, which for me is about as strong an endorsement as anything gets.