Imagine a company that makes cars sending out a message to all it's buyers saying "Hey, check out our competitor, you might like him". Imagine a car company helping another car company that is just starting, to grow faster and take more of the market.
That would be crazy. Because car selling, and most things, are a market that is fully served, and one where each person has a low appetite (aka one car and they are satisfied). If one person gets a customer, the other must lose that customer.
But with blogging, the amount of people who read blogs is growing every minute. The market is always getting bigger. And each person will read MANY blogs, and (if and when they buy something) buy from many teachers, not just one.
So, when a blogger helps another blogger get more audience and grow (by talking about him or giving him a guest post), the first blogger can only stand to gain.
The people who learn from the first blog will learn from the new blog, and the people who learn from the new blog (now and in the future) will likely be introduced to (and become readers/learners/buyers of) the first blog.
Also, the more people agree with you and blog about the same stuff, the more the people who want to learn what you teach will be able to find you and your brother bloggers, and so the more people will read/buy from you and other bloggers like you.
So, in the end, blogging is awesome because when one blogger helps another blogger, everyone (both bloggers, all alike bloggers, and all like-minded readers) benefits.
It's all benefit.
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