Writing a book is like having a baby. First you have this little idea the size of a pumpkin seed. You realize it might be best not to tell everyone. After all, you may lose it. It is not yet viable. Better wait and see.
Then you get to the middle stage and you realize it is kicking! It IS viable. It is alive! So you start telling people about it and you don't even feel so self-conscious about it any more.
Finally, reality sinks in. You are actually having this baby.