Here is an excerpt from an article written by Joan Magretta for the Harvard Business Review blog. To read the complete article, check out the wealth of free resources, and sign up for a subscription to HBR email alerts, please click here.

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I just finished a two-year project looking at Michael Porter’s most important insights for managers. Connecting the dots between his classic frameworks (the five forces, for example) and his latest thinking (the five tests of strategy) gave me a new understanding of the most common mistakes that can derail a company’s strategy. In a previous post, I focused on the fallacy of competing to be the best.

Here are [the first two of] five more traps I’ve seen managers fall into over and over again. Understanding Porter’s strategy fundamentals will help you to avoid them.

[To read the complete article, please click here.]

Mistake #1. Confusing marketing with strategy.

Correction: A value proposition isn’t the same thing as a strategy. If you’re trying to describe a strategy, the value proposition is a natural place to begin — it’s intuitive to think of strategy in terms of the mix of benefits aimed at meeting customers’ needs. But as important as it is to have insight into customers’ needs, don’t confuse marketing with strategy. What the marketing-only approach misses is that a robust strategy also requires a tailored value chain, a unique configuration of activities that best delivers that kind of value. This element of strategy is not at all intuitive, but it’s absolutely essential. If you perform the same activities as everyone else, in the same ways, how can you expect to achieve better performance? To establish a competitive advantage, a company must deliver its distinctive value through a distinctive value chain. It must perform different activities than rivals or perform similar activities in different ways.

Mistake #2. Confusing competitive advantage with “what you’re good at.”

Correction: Building on strength is a good thing, but when it comes to strategy, companies are too often inward looking and therefore likely to overestimate their strengths. You might perceive customer service as a strong area. So that becomes the “strength” on which you attempt to build a strategy. But a real strength for strategy purposes has to be something the company can do better than any of its rivals. And “better” because you are choosing to meet different needs and performing different activities than they perform, because you’ve chosen a different configuration for your value chain than they have.

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These mistakes are both common and costly. Getting smarter about how competition works and what strategy is will save you from making them.

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Joan Magretta is a senior associate at the Institute for Strategy and Competitiveness at Harvard Business School. She is the author of What Management Is and recently published Understanding Michael Porter: The Essential Guide to Competition and Strategy. To check out more blog posts by Joan Magretta, please click here.