Lesson #1 You don’t need a permission slip to run

I used to be an exercise-evader extraordinaire, the kind of woman who drove to the corner shop a two-minute walk away. Now, almost 18 years later, I’ve been transformed into someone who is so besotted by running that I’m just one marathon away from joining the 100 Marathon Club. When I think back to when I started running, aged 30, I realise that what delighted me most about it was that, unlike in my day job, I didn’t have to get anyone’s permission to do it. I just walked into the Definition Delicatessen, decided how I’d like to start redefining myself, and then pulled down the jar labelled “Runner”. Mainly because it sounded a whole lot more appealing than “Stilton-eating Sofa Surfer”. Yes, I’d have to pay the price required – the training, a few sacrificial toenails – but that decision didn’t require anyone’s approval except my own. The labels you desire may be “5K finisher”, “Sub-four-hour marathoner” or “Ultrarunner” – it doesn’t matter what you decide on, just make sure that, whatever it is, it truly tickles your fancy.

Lesson #2 You don’t have to love running to run

For every time that running is pure, undiluted joy, when I’m running next to someone chatty and floating almost effortlessly along, there’s a time that it’s so unbelievably hard it’s like bashing my head against a brick wall. I’ll be honest, at those times it’s only enjoyable when it stops. And that’s OK. Because if I add up all the amazing moments and then compare them with the number of hellish ones, the former outstrip the latter 1,000 to one. The combination of actually running and the feeling of having run have made me feel more alive, more connected, more brimful of happiness than any other activity on earth.

Lesson #3 Don’t worry that it won’t work out

We all know that in life there are only three certainties: death, tax and Tube strikes. Running is just the same: you can never tell whether you’re definitely going to hit your time target, manage a marathon or even get a medal. But don’t let that stop you from starting – like a love affair, the uncertainty is what makes it exciting.

Lesson #4 Speed isn’t the only way to measure your running success

I’ve come last in 24 marathons. But so far I’ve done 97 plus two 56-mile ultras. Does that make me a failure – or a runaway success? Many runners think that getting from point A to point B as speedily as possible is the only goal running has to offer. I happen to think differently. If you start measuring your success in races against different criteria – “most fun had”, “most friends made” or “best scenery spotted” – you’ll find that every race has PB potential.

Lesson #5 If it’s bad, it won’t necessarily get worse

Having finished the 91K/56.5-mile Comrades Marathon in South Africa twice, I now know this is 100% true. Even the legendary ultrarunner Ann Trason, who has won some of the world’s most challenging ultras, agrees: “It hurts up to a point and then it doesn’t get any worse,” she once said. Trust in this wisdom, write it on the back of your race number so you won’t forget it, and don’t let a fear of temporary pain put you off dashing after your dreams. Oh, and if all else fails, for pity’s sake, walk!

Lesson #6 Running doesn’t have to be boring

I simply don’t like running unless I have someone to talk to – and, truth to tell, a medal waiting for me at the end. So I no longer train but meet my buddy Belinda for a chat-run twice a week and do a marathon (or a long run with friends) every second weekend. I’ve become a champion chat-runner and if you find running tedious it may be time you became one, too.

Lesson #7 It’s not OK to moan while you’re running

I deserved the nickname Moaner Lisa when I whined incessantly during the Istanbul Marathon, and for the first time ever a runner literally sprinted to get away from me (at least that’s what it looked like). Heed the advice of Robert Louis Stevenson, who so sagely said: “Keep your fears to yourself, but share your inspiration with others.”

Lesson #8 Never, never, never try new things on race day

In the 2001 London Marathon I dressed up as one half of the Tortoise and the Hare fable without trying out my costume in training first. It turned out to be the papier-mache shell from hell and gave me unbearable backache. I ran the Stockholm Marathon with a spanking new bumbag – and it sanded a patch of skin the size of a pita bread off my stomach. I’ve had my arms almost sawn off by an untested T-shirt in the Eilat Desert Run in Israel. Just don’t do it!

Lesson #9 There are no limits

When I first started running I wholeheartedly believed 2K was my limit. I used to think I could only do one marathon (two at most) per year, until I realised I could safely do eight in 10 weeks, and 25 in a year. My new limit is 91K in one day. The more you do, the more you can do. By breaking any goal into bite-sized bits, anything is possible.

Lesson #10 Always share the joy

I’ll never forget the way my family, friends and colleagues shared their love of running with me, and encouraged me to join them. As the saying goes: “Friends don’t let friends drive … they make them run!”

Your Pace or Mine? What running taught me about life, laughter and coming last is published by Summersdale. Buy at the Guardian bookshop for £7.99