What’s striking about Fast Company’s 2013 list of the world’s 50 most innovative companies is the relative absence of large, established firms. Instead the list is dominated by the big technology winners of the past 20 years that have built innovation into their DNA (Apple, Google, Amazon, Samsung, Microsoft), and a lot of smaller, newer start-ups. The main exceptions are Target, Coca Cola, Corning, Ford, and Nike (the company that topped the list).

It’s not surprising that younger entrepreneurial firms are considered more innovative. After all, they are born from a new idea, and survive by finding creative ways to make that idea commercially viable. Larger, well-rooted companies however have just as much motivation to be innovative — and, as Scott Anthony has argued, they have even more resources to invest in new ventures. So why doesn’t innovation thrive in mature organizations?

To get some perspective on this question, I recently talked with Steve Blank, a serial entrepreneur, co-author of The Start-Up Owner’s Manual, and father of the “lean start-up” movement. As someone who teaches entrepreneurship not only in universities but also to U.S. government agencies and private corporations, he has a unique perspective. And in that context, he cites three major reasons why established companies struggle to innovate.

First, he says, the focus of an established firm is to execute an existing business model — to make sure it operates efficiently and satisfies customers. In contrast, the main job of a start-up is to search for a workable business model, to find the right match between customer needs and what the company can profitably offer. In other words in a start-up, innovation is not just about implementing a creative idea, but rather the search for a way to turn some aspect of that idea into something that customers are willing to pay for.

Finding a viable business model is not a linear, analytical process that can be guided by a business plan. Instead it requires iterative experimentation, talking to large numbers of potential customers, trying new things, and continually making adjustments. As such, discovering a new business model is inherently risky, and is far more likely to fail than to succeed. Blank explains that this is why companies need a portfolio of new business start-ups rather than putting all of their eggs into a limited number of baskets. But with little tolerance for risk, established firms want their new ventures to produce revenue in a predictable way — which only increases the possibility of failure.

Finally, Blank notes that the people who are best suited to search for new business models and conduct iterative experiments usually are not the same managers who succeed at running existing business units. Instead, internal entrepreneurs are more likely to be rebels who chafe at standard ways of doing things, don’t like to follow the rules, continually question authority, and have a high tolerance for failure. Yet instead of appointing these people to create new ventures, big companies often select high-potential managers who meet their standard competencies and are good at execution (and are easier to manage).

The bottom line of Steve Blank’s comments is that the process of starting a new business — no matter how compelling the original idea — is fundamentally different from running an existing one. So if you want your company to grow organically, then you need to organize your efforts around these differences.

Watch for Steve Blank’s upcoming article in the April issue of the Harvard Business Review.