Deadlines are essential when you are writing a book. If there are no deadlines, then the writer never tends to end their work. Without a deadline, the author will keep improving the prose or tinkering with the chapters of the book as there is always something that the author can change. A writer who works without a deadline is inviting trouble.
Check this to understand the importance of the deadline further.
Always start your book with a great idea. Every book writer has to start writing somewhere, and the best way to start is first to form a plan. There are book ideas that come in varied sizes and shapes, and you can get an idea for your book anywhere. You could get inspired by an article that you have read in the newspaper or a conversation that you had with your friend over a cup of coffee. Your idea for the book should be such that you can narrow it down to a few paragraphs, similar to what you read at the back cover of any book that you pick up. An idea is what will help you to start and finish your book.
Once you have an idea, you need characters to carry out your plan. Fictional books have characters. Non-fiction books also have characters, even if the characters in the non-fiction books are real people. When you form characters for your book, ask yourself what is so unique about the character. Figure out what the character aims to achieve and what are the obstacles that he has to face to reach his goal. Readers like characters that they can relate to, even if the character is flawed. So as the author of a book, you need to make sure that your characters are as impressive as can be.
Emphasizing on the need for a deadline when writing a book, it is essential to note that when you have a deadline in place, you tend to stick to it. It is something that differentiates serious and causal writers. Many writers start a book with all enthusiasm, but then they tend to find excuses about why they could not finish it. There could be reasons like health issues or family worries that are legitimate. However, if you are serious about writing a book, then this should be seen as a career, and you thus have to set time for it. If you have a deadline in place, then it will push you to write.