I don't think I've been in a meeting about a website or application in the last couple years where someone hasn't mentioned the Apple iPod or iPhone. I am starting to hear "We want the website to be simple, like Apple's stuff." as often as I hear "We need our site to rank high on Google."  But why does everyone love the simplicity of Apple products? Behind this praise is a great usability lesson that can be applied to websites and applications.

The funny thing about this is, the iPhone is not a simple device. It does some very complicated things for a phone: you can surf the internet, send email, find restaurants, take photos, listen to music.... sometimes all at once. And then you can buy an application that makes light saber sounds while you update your FaceBook profile (a good Jedi Knight is always plugged into his/her friend network). If the iPhone were a simple device it would have nothing but a clock, a phone, and maybe an address book. It is definitely not that.

Why, then, does everyone think the iPhone is so "simple"? Because what they really mean is that the iPhone is easy to use. All these great features might be hard to master on other phones, but even my grandmother could use an iPhone to check her email (and as research for this article, she will). In programmer-speak, it's a device with high "usability".

Why is the iPhone so Usable?

Let's look at the main iPhone interface and try to figure out why it's so easy to use. Here's a picture and quick description for anyone who hasn't seen one yet.

The iPhone Select an application by pressing an icon. To switch to another application, press the big button at the bottom and tap your next choice. No other menus, buttons, or shortcuts are possible. You're done writing email? Press the big button. Finished searching for local sushi restaurants? Press the big button.

It's pretty easy - when you want to switch programs, just press the big button and then tap the next program's icon. With most phones and PCs, this task is far more complicated because users have to look for the 'exit' button or decide which menu to open. The iPhone washes all this confusion away with one omnipresent button. Is this one button the reason for its great usability? It's an obvious place to start. A highly usable device or website reduces the amount of thinking its users must do, and only having one button definitely accomplishes that.

However, I think that this one button approach is not the reason that the iPhones is easy to use. Think of all the phones or appliances that only have 1-2 buttons but are still hard to figure out (ever tried to set the alarm clock in a hotel room?). If you look underneath this magical button, you find that the real reason the iPhone is easy to use is it perfectly models the user's thought process. The interface presents controls that correspond to the user's chosen task and current thoughts in a simple and easy to understand way.

Compare the iPhone to a PC

That might sounds like programmer babble, so let's consider an example. As a user, when you want to switch tasks on a phone or computer you have to (1) exit the current program and then (2) open a new one. The iPhone corresponds perfectly to these steps: (1) press the big button and then (2) choose a program. Other phones and computers don't quite have this correlation, which forces you to think more. If I'm using Excel on my PC and want to open Outlook, here are my options to accomplish Step 1:

1. Navigate to my desktop and look for the Outlook icon.
2. Go to the Start menu and look for Outlook in my programs list.
3. Press the hot key on my keyboard that I assigned to Outlook.
4. Close Excel (wait...should I save?). 
   
5. Try to remember if Outlook is open and then press alt-tab.
6. Look at the Taskbar to see if Outlook is open and then click on it.
   

My PC seems to require a lot more thought to complete this task than the iPhone. Only option #4 is anything like Step 1, but it will distract me with messages about saving my Excel file. Option #3 is also pretty good, which shows why people like shortcuts (no need to deal with all these other steps). But none of these really match the task and thinking in Step 1. Plus, many of them require multiple steps or special configurations (shortcuts have to be created, for example). Deciding which of them to pick and how each relates to my task makes me ...have to think. And thinking is work, which means I will forever say that using a PC is harder than using an iPhone.

Conclusion: Learn How Your Users Think

Let's  review what we've learned:

1. The iPhone is a pretty complicated phone, but people find it easy to use.
2. It is easy to use because you don't have to think very much - it takes minimal effort to choose what you want to do, and then do it.
3. It accomplishes this because its interface matches the user's thoughts and goals in a simple and correct way.

When people crave "simplicity" in a website or application, what they are really seeking is a highly usable interface that reduces the amount of thought users have to put into each action. Accomplishing this means that people find your software easy to use and full of delightful features. We don't want simple devices or websites, we want ones that make complicated and amazing tasks very easy.

Usability at it's finest, and the iPhone definitely deserves its kudos.