According to Joe Pulizzi, the problem isn't the quality of the content marketing produced, it's consistency.
The two main reasons, in his opinion, for companies failing in their endeavours is 1) not documenting their strategy and 2) not following their strategies.
There's also a nice bit of debunking in there about content marketing. It's not just blog writing!
Many marketers believe that content marketing only includes digital. This couldn't be further from the truth. Content marketing includes digital, print and in-person content that is NOT ordinarily about our products and services. It's content that is useful and wanted by the audience, and causes the reader/engager to know, like and trust the company creating the content, which leads to positive buying behavior in the future. Think of it like a content platform, such as American Express Open Forum, a magazine, such as Airbnb's Pineapple, or a content-focused event like Dreamforce from Salesforce.com.