I used to think that my manuscripts were the best things ever written. I didn't need to edit them because they were already perfect as they were. I didn't need to be in a crit group because they couldn't be improved upon.
In short, I had mis-placed confidence in my manuscripts.
SCBWI has gently encouraged me to not be so precious about them and that editing really was worth doing. They've encouraged me to join a crit group and to take the feedback on board - they've given me constructive crits instead of the put-downs I was dreading.
I've learnt from other people's writing and I've learnt how to improve my own writing by reading the feedback.
It's not cheap to join SCBWI, but it's so worth it within the first few months so I really don't mind paying the annual fee and I recommend it to anyone who will listen!
I've learnt about new agents and publishers as soon as they go public with their opening.
I'm one of the first to know about slushpile challenges and competitions and limited opening submissions. I've learnt about agents and publishers to go with and when really big agents and publishers are open for a new author to take on.
I've learnt that it's OK to cry when you're rejected and I've learnt to submit to the next one on my spreadsheet as soon as I get the rejection email.
I've learnt that it's OK to admit that you aren't perfect and that you need help... everyone does at some point and SCBWI is the best place I've ever found to help to get you to be the best you can be.
If you write or illustrate for children, get thee to SCBWI and they will help you to be the best person you can be!