Here's why: It's because if you're serious about making money online you should be playing to win.
This means you want to find where you have an advantage over your competitors. Just like in sports, you exploit your advantage to win the game. If you're playing basketball, a smart coach isn't going let his best post-player shoot threes all night just because he loves and is passionate about shooting threes.
And, in the internet marketing niche people fail over and over again because there are passionate about learning how to make money online. So, what do they do? They start a blog about how to make money online even though they haven't made money yet. This is recipe for failure. You're always going to be playing from behind that way.
What you should do is assess your strengths. Ask yourself what are my strengths? What are my talents? What are you skilled at? Find your strengths then, leverage them to win in market with buyers.