You should take it as a sign that the reader felt that the post was not useful. If that's something that's worth taking personally...then you can take it personally. I know I've at times felt that the fact that I provided a post that wasn't helpful to be a failure, and taken it as such. But of course there were other times where I haven't felt that a given person's opinion on the quality of a post is a reflection of me. It's a decision you'll need to make, and for each post.
Importantly however is to not just wallow in the fact that someone feels your post isn't useful. You have been faced with a problem; fix it. Work to figure out why others don't feel your post is useful, and fix those problems, whether it's a lack of information, too much information, a lack of clarity, poor presentation of your ideas, poor research, or any number of other problems.
Don't get mad at others for telling you that your post has problems, be thankful that they've taken the time to give you feedback, and use that feedback to improve your post. That is the most important thing to do. Whether you end up getting upset at yourself for having made a mistake that you needed to fix or not is not particularly important, what's important is that you fix it (or make your best attempt to do so).