Thirty years ago, Suzanne refused to help another writer because "she'll become my competition." I didn't agree then; I strongly disagree today.
I believe in the principle of giving ourselves freely and sharing what we know. I don't think of others as my competition. I think of them as other writers who are trying to sell what they write. I want to help.
Here's my favorite verse that's not from the Bible: Yea, the Lord shoveleth it in; I shoveleth it out; and behold, the Lord hath a larger shovel (Jubilations 4:4).
To the fearful and insecure, it may sound outrageous to give away what we've worked hard to learn. But it really works the other way. I'm a giver and I like to give. As I examine my writing career, every upward step I've taken has come about because someone else opened the door. My first book publisher and my first agent came because someone else opened the door. In both instances, the help was from individuals I had helped but never expected any return.
Professionals know that. They enjoy sharing what they know and giving to others. That puts them in a position to receive from others.
We receive by giving; we grow by sharing.