One of the hardest things I had to do as a doctoral student was to learn how to invite and encourage criticism of my work and then take that criticism and use it constructively. It was really difficult. My inner critic was already harsh and hard to silence. I felt I couldn't pass anything to anyone else to read until it was perfect. In practice, this made it hard to ever pass anything on at all.
After I did finally pass any bit of writing along, I didn't accept critical comments, however constructive they might be. My insecurity was such that I only wanted to hear good things about my work. I would get defensive even at suggested changes, making it harder for my writing group and advisers to give me honest comments and impossible for me to benefit from hearing and reading their ideas.
This was, of course, my loss. I've come to learn that someone who is willingly reading over my work and giving me their honest impressions and constructive suggestions is giving me a great gift, especially if they have some knowledge of my discipline. From the other side, I know it's a lot of effort (though sometimes also fun) to read someone's research and offer constructive ideas for revision. I'm not excited about doing it if I know the person is going to be defensive or even hostile about any criticism.
What I've learned is to take a deep breath and give my writing to others to read. Even more important, I've also learned how to listen to their criticism and suggestions not as evidence that they think my writing is terrible, but as ideas of how I can make my writing better, clearer and more organized.
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