Writing online is rewarded only if you can get traffic, and the more traffic you can send to your site the better. People cannot but products that you are showing if they do not get to your pages. Adsense only pays if people view, and hopefully click, an ad. So, writing and not promoting is about as effective as writing and not posting at all. Even if you are just writing to get a message out, like promoting environmental responsibility, you have to bring in readers, or you could yell your message out in the middle of a forest with about the same impact.
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