For first-time Marathon runners, agreeing to run their first 26-mile race is the easy part.
Rising to the challenge of tackling London, or any other marathon for that matter, is often taken under the not inconsiderable influence of alcohol or the emotional pressure of running for charity.
But the euphoria is soon washed away by the enormity of the decision, prompting a mad spell of panic over how best to cope with the challenge.
For marathon runners, the shelves of the leading book stores are positively bulging with advice from some of the most respected names in the business.
But to the first-time runner, standing like a wide-eyed rabbit caught in the glare of a car's headlights, the advice can be a little too professional.
So here, from one plodder to another, is BBC Sport's back-to-basics London Marathon survival guide.
Not everyone eats breakfast before a big run, but it is essential to get a good feed inside you to act as fuel for the road ahead.
I wouldn't recommend a full English and a pot of coffee, but a bowl of porridge, a few rounds of toast and some orange juice or water will serve you well if your nerves allow.
Don't wait until you are thirsty to drink
Drinking plenty is essential, not only before the race but during the event itself.
Take on plenty of water as you make your way to the starting area on Sunday morning and accept water and sports drinks every time they are offered during the race, even if you are not thirsty.
If you are thirsty, you are already dehydrated, and the results can be disastrous.
Try to enjoy an atmosphere you will never have experienced before. In truth, you probably won't be able to help but enjoy it.
The crowds lining the streets of London, and the sights you pass, will be enough to put a smile on your face for the early stages at least.
Do some sightseeing
Take time to take in the sights
There are so many landmarks on the London Marathon route, but it's easy to find yourself so focussed on running that you forget to look around.
Looking forward to tourist spots such as the Cutty Sark and the London Eye will help take your mind off things and set manageable targets to break the route up.
Walk if you have to
For those who don't expect to post a time that will trouble the scorers, completing the course without walking can be the next challenge.
Running every step of the way is a major achievement, however long it takes, but there is no shame in walking if you need to.
If the effort of running becomes too much, allow yourself a bit of a breather, while it can also help to build in planned walking breaks at certain mileage points.
But try to make it a brisk walk, as it can be hellishly hard to get going again once you have ground to a halt.
The previous two plans can both help break 26 miles down into more manageable pieces, but simply having a mental plan of your race will help you through.
Standing at the start line and thinking about the finish is daunting, so tell yourself you are running four six-mile races, followed by a two-mile warm down.
Alternatively, break your day down into five decreasing distances of eight, six, five, four and three miles.
Once the waiting is over and the congestion has calmed down, the temptation is to push on and get some good early miles under your belt.
Don't be tempted to sprint through the pack
But pushing too hard in the first six miles will destroy you for the last six.
Allow runners who look slower than you - including the Wombles and the rhinos - to breeze past you and simply tell yourself that you'll see them all later when you are cruising past them in the closing stages.
Every mile is decorated by an archway of balloons. Celebrate each one as a major achievement.
But don't start at one and count up, work your way backwards so you can picture the distance melting away.
Throw your arms in the air, leap through the archway or shout out in celebration. The less animated among you may simply like to mentally tick another mile off the list.
Do it for charity
Running for charity is rewarding for both of you
If you have come this far, you might as well let someone else benefit from your efforts.
Choosing a charity to run for keeps you going when things get tough and gives you double the satisfaction when you cross the line.
My nominated charity was Daisy's Dream, a support organisation for bereaved children who have a team running again this year.
Stick with what you know
Wear the trainers and the kit you have worn during your longest runs, don't be tempted to treat yourself to anything new for your big day.
New shoes will give you blisters and clothing you are not used to may rub or chafe.
If you have tried jelly babies or gels for a training run boost, stick with them, but don't accept promotional giveaways from the sponsors if you have never tried them before as they may not agree with you on the day.
Remember the prize
Keep dreaming of your ultimate prize
Whenever things get tough - and they will - imagine yourself striding across the finishing line and being presented with your medal.
You will probably tell yourself you should have trained longer or harder, but every runner alongside you is telling themselves the same.
Decide what you will reward yourself with after the race, whether it's a hot bath or a cold beer, and think of that every time you are feeling negative.