I'm honestly not sure why I'm running the London Marathon. And I'm desperately trying to keep it that way.
If there's one thing I've learned from training for my first London 26-miler for the Mental Health Foundation - beyond a few new, largely subconscious and biological techniques to ensure I keep breathing and moving after two dozen miles of hard road - it's the importance of tactical stupidity. That sometimes you just have to just do something. You just have to start, and keep going, and forget that it's totally pointless.
If I think about the event itself too much - about the potential medical implications, the inherent, for me, vanity, or about the inevitable anxiety involved in asking for sponsorship money and the transparent fear of my own mortality I am confessing to, and re-enacting, each time I take a step towards the finish line - I find it hard to justify.
The usual arguments for 'doing' a marathon just don't add up, to me, on close inspection.
Is the act of making it through 26 miles an achievement in and of itself? Does it count as a 'life milestone', like publishing a book, having a child, or reaching your hundredth birthday?
I don't think so. At least not usually. Yes, it's a long way to run. But it is hardly very remarkable, on a macro scale. Thousands of people run 26 miles every day. Thousands every year run double, even triple that distance - and do it through burning hot deserts and Arctic Tundra. I recently described my training regime to a fellow runner who nodded sympathetically and then told me that they were also running a marathon, only that they were running it through the Amazon Rainforest. That shut me up. Though, on reflection, it occurs that the threat of being chased by a slathering puma would surely make it easier to complete the distance?
What about the health argument? Well... I'm not sure I buy that either. Yes, exercising regularly is obviously a benefit to your health - and it's made me more aware of my diet, in as much as my weekly hamburger habit has been reduced to a mere fortnightly dalliance - but justifying the marathon as a way to 'keep fit' seems dubious in the face of growing evidence that not only can it lead to serious injuries - and thus greater periods of inactivity over the long term - but also a shorter lifespan by definition.
Then there's the charity element. Yes, the marathon raises vast amounts of money, particularly in London. Yes, I feel like I'm running the event for a worthy cause, and a charity I hugely admire. But could I not, if I felt like it, raise the money for a charity in my own time, apropos of nothing? Could I not just sacrifice chunks of my salary each month, quietly, without writing blogs about it on a major news site, and without traipsing around London in tights every other day for six months? Yes, I could.
So why do it?
Honestly, most of the time, I'm not sure. And it's at that point I put on my trainers, go running and - for whatever reason - I stop caring.
The anxiety that clouds my brain on a normal day evaporates. I just keep moving. I traverse the City, Westminster, Greenwich and Tower Bridge. I pass old workplaces, pubs I last visited on disastrous first dates a decade ago, street corners crowded with ghosts of 30 years, and then I run away from them all and carry on down the road. Eventually, I stop thinking; my mind diffuses over the town, and I let everything go.
It's not easy for me to get into this state. I'm restless and anxious, by default, and often distracted. I am not religious, and every time I've tried to mediate I just end up falling asleep. But when I run a long way - after about 10 miles, usually - the world literally changes. It opens up and swallows me, and with the help of old friends on my headphones I fall into it gladly.
That's something quite special, for me, even though - perhaps because - it is also inexplicable. And, in a very small way, I think it helps me understand something of the work of my chosen charity.
When I signed up for the marathon, it was largely to see if I could get a place. When I agreed to go through with it, I'm pretty sure I was just afraid to turn 30, and when I started the training it was just to prove I could.
But now? Now I'm running it because I don't want to know why.
I keep going, through the back injuries, the colds and the stinking kit, the inedible energy gels and the tedious training plan message boards, just because. Because there is peace out there, in the momentum of the mindless miles. So if you see me on race day, please don't ask why I'm there. If I ever figure it out, I might not make it all the way around.