As authors, this is something we hear often, but I sometimes wonder if this is something that should always be necessary. When I hear it, there are times I feel those who say it are trying to give themselves permission to be rude and well… a jerk.
It is necessary when it comes to professional reviews and feedback. You will probably hear things you don’t like, but most of it will be constructive. These are the things we need to take to heart because it can help us greatly improve our writing. So if someone is giving you constructive criticism, even if you feel like telling them where to go at that moment, stop and consider what you can learn from them and thank them for the feedback.
You will also often get not so nice comments about your work, and it may not be constructive, but we have to remember that not everyone is going to like our work. Do you like every book you read? I know I don’t. And I’ve read things (like Twilight) that I loved, and a lot of other people hated. It happens and you can’t get around it. If people make negative comments about your work just because it’s not their thing, well… in truth, that’s their problem and not something you should concern yourself with. They don’t have to like it or read it.
There are others, however, who just say negative things about authors for the sole purpose of causing harm. Sometimes they even work in groups. These people are cyber-bullies. While you should just ignore what they say (at least online… as in don’t engage them publicly), it can be hurtful. If you’re affected, I don’t believe this is the time to “grow a thick skin.” Talk to friends and other authors (that you know and trust) about how you’re feeling, but do it privately. They can help you cope.
Growing a thick skin doesn’t mean you should ignore how you’re feeling when you’re being bullied or attacked on a public forum. What it does mean is that you shouldn’t let constructive criticism bring you down. Learn from it and allow it to make you a better writer.