Ok, so I can't deny that blogging makes a lot of people a lot of money, but it's not all it's cracked up to be. There's a myriad of blogs out there with sensational claims but it's what they're not telling you that's important.
For every blog that suceeds, there are 1,000 that fail
Well depending on your definition of fail, there's even more than that. The majority of beginner bloggers assure themselves that their blog will succeed, and it's true that you need this kind of 'can do' attitude. Deep down though, every beginner believes that they will be earning enough money to change their life - be it one month from now or 5 years. The vast majority of blogs do not earn the author any money whatsoever, and the ones that do may only earn just enough to cover the monthly hosting payment.
You don't know if you will succeed until you try
The problem, (or success depending on how you look at it), with the internet is that no matter how hard you try, you may never really have that break-through that you're after. You can spend hours each night trying to get more than a 1,000 strong community, while someone else gets 6,000,000 YouTube hits for falling over. The unpredictability of your success works in the advantage of the blogger. They can talk you in to giving it a try; and rake in their $100 commission of course.
For every hour you think it will take, it will take 3.
Bloggers make a hard sell with the idea of passive income. Yes, you can generate a nice stream of money while people read what you've typed one year ago, but blogging involves more than just what meets the eye. Every successful blogger spends more time preparing and promoting each article than the do actually writing it. That's not to mention managing the community, e.g. filtering comments/answering questions, but also providing a consistent presence on social media. Articles link to specific keywords, and are often accompanied by promotional articles on several other sites.
Be prepared not to be supported
Many people, especially those who aren't technically-savy, don't understand how you can make money online and won't offer you support until you can prove them wrong. Even when you start earning a couple of hundred extra dollars a month, you'll still get the occasional "Isn't it time you got a real job?" comment every now and then.