I hate waiting.

By far, the single worst part of writing a book is AFTER you have completed the book.

First, you have to wait for a proof.
Then you have to wait for editors to do their thing.
Then you have to wait for friends and family to read the book. (Hint: sometimes this takes longer than actually writing the book)
Then you have to find a literary agent.
Then you have to wait for agents to reply to you - IF they reply to you.
Then you have to make changes based on the feedback of all the above people.

Then, if you are lucky, you get to publish your book.

Besides that, it's EASY!