In the bestselling book It's Not What You Sell, It's What You Stand For, author Roy Spence makes the case that all extraordinary businesses are driven by purpose.

Spence has tested that theory by helping companies like Walmart, BMW and Southwest Airlines excel in their industries--by obsessively focusing on purpose. According to Spence, if a company is able to keep an eye on its purpose, employees will be more engaged and innovative, the competition will be less threatening, and customers will keep coming back for more.

Thanks to Roy's compelling thinking, executives are now seeking to define their company's purpose. And the timing couldn't be better. The new millennial workforce and social media-driven consumers are increasingly attracted to well-articulated corporate purposes.

So how does one go about finding a company's purpose?

At the onset, discovering a business's purpose sounds like a simple proposition. Most companies have already spent a few hours fine-tuning their corporate mission statement to produce something that may resemble a purpose. After all, a purpose isn't much different than a mission, right?

Executives who think this way often grossly misidentify their company's purpose. A mission statement describes a company's function, markets, competitive advantages and goals. A mission statement is academic, precisely measured and lacks verve. It's flat.

But a purpose statement has soul. A purpose statement answers the question of why we even do this stuff in the first place. A mission describes the allied forces taking Normandy while a purpose describes preserving freedom. A purpose describes what internally drives a team forward at a gut level. And it can't just be for the love of the money.

To truly answer the question of purpose, a company must take that pretty green stuff out of the equation entirely. Yes, this can be very hard to do. But give it a try.

Try taking on a child's mindset to help define your business's purpose.

Imagine you're all of 10 years old and building a fort with your best friends. You're not building just any fort though. You're building a tree fort, and tree forts are the cooooolest. Once complete, it will sit high in a treetop above everything and everyone--a refuge for you and your friends.

You're having the time of your life building it and not making a dime. You'll work from morning until night , or until Mom calls you in for dinner without even realizing time exists. You're fully engaged. Problems like bad weather are dismissed without a moment's notice. The rain just makes the challenge all the more enjoyable. You and your friends are the best team on the block, laughing and working as one.

If you've never built a tree fort, then imagine any epic challenge you took on with your friends just for fun. Starting a garage band is another great example.

The tree fort your company is building is its purpose. It may be hidden under heaps of clutter, financial statements and red tape, but it's definitely there. It may even be blindingly obvious, but just a little too obvious to clearly identify.

If your business didn't have a purpose, it wouldn't exist.

A purpose can be heavily masked but it's always there, pushing the company and your team forward. Businesses grow when like-minded people have fun creating something that inspires and unites them.

So, find the tree fort your business is building. Find it, create an image that represents it, and hang it on the wall next to your sales projections. Your purpose is more responsible for your sales than any competitive advantage or smart marketing campaign. Your purpose preceded them and defined them, and will continue to feed them if examined, contemplated and felt each day.

If you have difficulty clearly defining your company's purpose, then just remember to approach every day with a 10-year-old's passion for building the coolest tree fort on the block. A combination of enthusiasm, teamwork and inspiration will bring your company's purpose back to the surface, and once identified, it will always steer your business in the right direction.