You will think all those poncey runners spending hundreds of pounds on trainers are ridiculous. You will spend as little as possible. You will regret this when a mere month later you've done in your ankles and can't run at all.
5k will initially seem like an insurmountable distance. You will surpass this quickly, and amaze yourself.
Running is more addictive than chocolate and cigarettes and any other vice you might be harbouring.
Every run will not be faster than the last, even though you want it to be. Sometimes your body's tired, sometimes your mind's tired. Sometimes you just suck. It doesn't matter, you're still running. Tune out the Nike lady telling you how slowly you're going every mile and just enjoy it.
I cannot run with other people.
You may start to eschew Zara and Topshop in favour of Nike and brightly coloured sports bras.
When you get injured, and you can't run, you'll sink into a kind of running related funk. Non-runners will think you ridiculous. Other runners will get it completely.
Forrest Gump moments do happen. Embrace them, but not too much. Beware the overtraining injury.
You will get injured. Often.
When you overtake a fellow runner in the park you'll feel a wicked sense of joy. However, when you're not running, you'll feel a weird sense of solidarity with whoever runs past you, and silently cheer them on in your head.
When your old shoes are knackered and it's time for a new pair, it's bizarrely unsettling. You have to say goodbye to your trusty companions that kept you company for all those miles, and even if sometimes they gave you blisters, and you suspect they were partially responsible for that injury, you'll keep them around for as long as possible. What if the new pair aren't as comfy? What if they rub and give you a whole new set of blisters? What if they bring back the shin splints? I kept my old shoes hanging around unused in my room for about a fortnight. Just in case.
That said, taking your shiny new trainers on their virgin voyage makes you almost giddy with excitement.
People might start to worry that you're addicted. You are.
You'll have a perfect run in your head. That distance, that time. You'll get there one day.
Sometimes, going for a run will be the only time in the day that you have the headspace to think. Sometimes, it'll be the only time in the day where you can properly switch off and not think.
It is therapeutic. But sometimes it's a battle. When you're a mile from home and you feel like your body is broken and your mind is incoherent and fragmented in its exhaustion, it will take all your mettle to get you to your door. You might cry. But when you get home and you get into the shower you will feel like you're floating. And not just because you can't feel your legs anymore.
Running in the rain. Bliss.
On the odd occasions when you have a really good run, and you smash that PB, you'll be elated for the entire day, and you'll feel like you can do anything.
And that's why I run.