Is it easy to make money from a blog?

This is a wishful blog that wants to make a decent life from his / her blog. Before you start anything, consider the following:

1.) I think the subject of your blog. This is usually something you love. It's a good start, because that means you will not boring articles for your blog! In fact, it does not even feel like work! But if you want to make money from your website, you have to think about it very carefully. The bottom line is this: Is there enough product that you can recommend related to your subject?

Let's say you are interested in deep-sea expeditions. You are fascinated by the ability of high-tech million dollar submarines and their dive depths over 1000 meters. You set up a blog, there are a lot of submarine adventure, deep sea creatures and other fascinating articles. Now you want to earn some cash from your website through affiliate marketing. You can not find anything about deep-sea adventure products, so you throw a few ad washing machines and fixed. I do not think i need to tell you the title here! How much will you make? Zilch possible.