Why do so many people get banned from google adsense?

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I am really looking forward to making money with google adsense. But i hear so many stories of people getting banned. And a lot of the time they say for no apparent reason. Or for unfair reasoning. I also hear how very strict Google is with earning through adsense. All this actually has kept me away from even going near google adsense. Does anyone else feel the same way? Does anyone have any encouraging stories to share about google adsense? How about some good experiences? Or maybe you use an alternative like Microsoft adcenter, how is that in comparison? Any thoughts would be lovely.