Think of a cow.
Got one?
Now imagine that we are in conference room full of people and I've asked everyone to think of a cow.
Is everyone on the same page?
Arguably, yes. After all, I didn't just ask them to think of an animal, or even a barnyard-type animal. I asked them to think of a cow. So everyone is thinking about the same thing, right?

Well, what color is your cow? Where is it hanging out? What is it doing? Is it fat or thin?
What about the other people in the conference room? are all of their cows similar to yours, or slightly different? Picture the little imaginary herd that all of you have created together. We've probably got some brown cows, some black and white jobbies, maybe a black one. Some are laying around in the distance, some are up against a fence nibbling hay out of our hands. Some are in a barn, some are hooked up to milking machines. They're fat, they're thin. They're cute, they're gross, they're something familiar, they're completely foreign. They're all of these things all at the same time.

So everyone in the conference room thinks they are thinking about the same thing. But what if someone asks about the hooves of the cows? One cow probably hasn't had its feet looked after in a long time. Another spends most of its time indoors and her hooves get irritated by the cement floor of the barn. Yet another has shiny hooves that are regularly rubbed with organic linament by her proud owner. Each cow is different in her details, and each cow-imaginer can easily zoom in and argue for the importance of his or her cow's hoof details.

Companies do this all the time, every day. Everyone thinks they are thinking about 'the user.' Guess what? Everyone's concept of the user is slightly different. These differences are further hidden by slightly more detailed language, like 'the administrator' (talking about users in terms of roles) or 'the early adopters' (defining segments of users).

So long story longer, this is why personas are so important. And this is why I'm convinced that, in a way, it doesn't matter who your persona is as much as it matters that you have one. The lack of shared focus between a team of people who are all working on the same product can be so detrimental that it can trump any 'bad' effects that could be caused by using the 'wrong' persona. In other words, even if they are building a product for cows, if everyone focused on the exact same horse to build the product, they'd be better off than if they were all focusing on different cows. Why? Because at the very least, the resulting product would make sense end-to-end. And a product that makes sense end-to-end for a horse is probably better for cows than a product that is good for some cows some of the time, and other cows some of the time, and so on.

Whew, the farm is getting full.

One last thing:

If I ask the same conference room full of people to picture a brown cow, a pretty chubby one with a swayed back and a full udder, chewing peacefully on a mouthful of hay in a large paddock that has a few other cows in it, flicking its tail against an annoying horsefly, you're probably willing to give up your original cow and start thinking about mine. It's not such a big deal...it's still a cow, and if I tell you that I've done some research and most of the cows in our target market are paddock-dwellers with swaybacks and active tails, you'd believe me.

Now, when we start to talk about the barnyard features that we should build to support our cow's hoof-related requirements, all of us can zoom in on this cow's hooves and make some sensible decisions. We won't end up building hoof features for indoor cows and udder features for outdoor cows.

By the way, in my experience, stakeholder-type people aren't terribly attached to their own cows. As long as they get to say 'hey, this is what my cow looks like', and they get to add their opinions into the mix, and they get to hear the relevant cow-data, they're pretty willing to give up the black and white for brown, the barn for the paddock, and the oats for the hay.

User is a four-letter word. But cow is not. And neither is "Sarah, the spendthrift."

Anyways, I could have avoided typing this whole thing and simply provided this excellent quote on user experience by one of the pioneers in our field, Dr. Seuss:

"A moose is asleep.
He is dreaming of moose drinks.
A goose is asleep.
He is dreaming of goose drinks.
That's all well and good when a moose dreams of moose juice.
And nothing goes wrong when a goose dreams of goose juice.

But it isn't too good when a moose and a goose
Start dreaming they're drinking the other one's juice.
Moose juice, not goose juice, is juice for a moose.
And goose juice, not moose juice, is juice for a goose.
So when a goose gets a mouthful of juices of moose's
and moose gets a mouthful of juices of goose's,
They always fall out of their beds screaming screams.
SO...
I'm warning you, now! Never drink in your dreams."
Dr. Seuss's Sleep Book, Theodore Geisel, pp 42-43.