As a writer, you are a unique creature. While you are producing a product that can only be interpreted so many ways, you are also crafting materials for (or with) someone else with the intent of selling it somewhere down the road.
If you intend to make money selling your work, you had better learn how to take criticism.
The thing to remember here is, the minute you “publish” your work–it is no longer about you. Once you breathe life into tired words, crafting into a story or an interesting article to be published online or in print, those words have to grab and engage the reader to sell copies, communicate a point, or seal a deal.
Since writing is a solitary activity, not having human contact while you’re working on a project can put blinders on you, causing you to be more possessive about your work than you need to be. Instead of looking at your work objectively, you end up looking at it subjectively and can no longer see clearly.
Another reason why writers take comments too personally is simply because they don’t perceive writing to be a business. Any business owner, regardless of how big their ego is, would be concerned with the bottom line. In other words, if you are a writer who wants to sell books or articles, then why wouldn’t you listen to your customers to deliver the best product?
If you can’t take legitimate, honest criticism about your work, then don’t plan on writing professionally. Period.
There are ways to improve your ability to take criticism. Try joining a writer’s workshop like Critters.Org. I’ve had several good experiences with this because any time you throw up a story on this group, the standardized bell curve rings true. You’ll get fans of your work; you’ll get people who hate your work. Those people you want to ignore. The gold is in the middle, where some writers will talk about both the good and bad points to your story. If online workshops aren’t your thing, try face-to-face groups or public speaking events.
If all else fails, when you hear someone criticizing your work, BREATHE. Write the comment down in your journal. (I highly recommend carrying one with you at all times.) Then, after you’ve had the chance to get on with your day, revisit the comment and make a decision whether or not the comment was valid, who said it, and if you should take it seriously.