Childhood toys make useful analogies, as everyone understands how they work.
Well Nick Usborne, from marketingexperiments.com, has discovered that e-commerce websites are just like toy cars.
You know the ones where you push the car repeatedly forward a few times, keeping hold of it?
The energy from your arm is transferred to a small flywheel in the car. So when you finally let go, the car speeds across the floor and smashes into your mother's best dining room furniture.
So long as it doesn't bump into anything, the car keeps going until all that kinetic energy you put into it with your arm is expended. So why doesn't it keep going forever? Because of friction.
And this is exactly what happens when people go eshopping.
If you want someone to complete a process, you first have to provide them with enough energy to overcome the inherent friction of the process itself.
A great deal of research has been done on shopping cart abandonment. Typically, when a hundred people start buying something online, of those who do not complete the purchase, seventy gave up somewhere while on the shopping cart pages.
Why? Too little energy. Too much friction.
As a formula, it is easy to visualise. In order to maximise the success of your site you need to increase the energy you transfer to your visitors, and reduce the friction within the page or pages on which the visitors have to do something.
In particular, this means that if the purchase process is lengthy, you had better be sure that you have transferred a great deal of energy to the buyer before they begin.
Too often the energy from a home page or second level page is spread too thinly across too many topics.
If you want someone to do something, you need to build what amounts to a funnel, or pathway.
Help the reader identify the one thing they want, and then simplify and "narrow" the design and the text in order to focus on that one thing, and build energy and enthusiasm within the reader.
Take away any distractions, visually or with words. Focus on the one thing.
And when you come to designing and writing the shopping cart, reduce the amount of friction by as much as you can. In other words, ask for as little information as you can, and reduce the number of pages to a minimum.
You need your reader to have completed the process before that kinetic energy has dissipated.
This applies to any website where there is a call to action, such as subscribing to a newsletter or applying for an account, not just shopping sites.
But if you use this thinking throughout your website you will find places where you can increase the transfer of energy to your readers on the sales or information pages, and reduce the friction on the sign-up, application, or shopping cart pages.
So the number one rule for any web designer must be: "More energy. Less friction".