Back in January when I slogged up the inclines in St James’s Park in London wondering how they could be so vicious and yet so invisible, the celebrity trainer Matt Roberts told me that you had to find your motivation in running. Not many people enjoy it for its own sake. “Is there a charity you really care about, something you could support for a sponsored 5K?” he asked. Hard to know how to answer this. It made me think of David Cameron (Roberts was his trainer, remember), a feckless, unpatriotic man, indolently spoiling everything for everyone, then taking a break to puff his way round civic spaces and congratulate himself on his life choices, self-love cloaked in self-righteousness. “Sponsored runs make me feel sick,” I said, but Roberts could see I felt sick anyway with the exertion and discreetly looked away.

I solved this – did I solve it? You decide – by doing a run for a charity I didn’t care about and not registering, just paying 20 quid on the day. It was the wrong choice, in many ways, because it was a 5K, 10K and 15K run all setting off from the same place, and I felt intimidated by the 10Kers and 15Kers, by everyone in matching T-shirts, by the apparatus of the “fun run” (loads of tape, like a crime scene), and the fact that I was the only person who didn’t have water. Oh, and also, I never got beyond week five in the eight-week Couch To 5K programme. I had an injury, then there was the snow, then there was more snow, and I ended up doing week five again and again.

However, that topped out at a 20-minute solid run, and a 5K, unless you’re pretend-run-walking, shouldn’t take more than 32 minutes. It is a great misconception (of mine) that exhaustion moves in a linear way, so at 17 minutes you’re 8.5 times more exhausted than at two minutes. In real life, I have a point at three minutes when I think I can’t go on, and another two minutes before the end. It’s like needing a wee or missing your kids: you can cope fine until it’s almost over, then you can’t cope at all.

The first kilometre was much shorter than you think. When you’re accustomed to measuring by time, the switch to measuring by distance is cognitively liberating, like counting calories and suddenly switching to counting carbs. The second km is challenging, as it dawns on you that there are three more to come: concentrate on scenery. Never fixate on getting to a point, and how many times you need to get to a similarly distant point again. The third km tips you over into nearly there territory, especially if you’re no good at maths. The fourth km is where you register unfamiliar thoughts, such as “I could probably go a bit farther than 5K”. The fifth km you realise you couldn’t.

I did it in 32.46, an average of 6 mins 24 secs a kilometre: not impressive, but running not walking. In short: under-prepared, under-motivated, under-buddied, ill-equipped. That’s how I started. And I ended on top of the world, ladies and gentlemen.

What I learned this week

Make a friend, to run with. The people with friends had a lot more “fun”.

• Zoe wears top, Bellum Active Endurance Run Top. Leggings: My Gym wardrobe. Trainers: Saucony Triumph ISO 4. Hair & makeup: Sarah Cherry