I'm puzzled by the "share-alike" clause in Creative Commons license. This license allows free commercial use but "require[s]  adaptations of the work to be released under the same or similar license as the original".
So if I'm building a commercial product with proprietary content and I use a CC BY-SA work, does that mean that I have to make my entire product available for free download?
If that's the case, then I can see how this would work for a commercial company that, hypothetically, sells printouts of Wikipedia pages. But how would it work for a commercial company that builds its own content? Seems to me that if my product is content I have to stay completely away from CC BY-SA works. Am I correct?