Many writers starting out on their first book are put off by the idea of writing an outline first. Indeed they object to anything at all that isn't actually writing the book. Most understand that they will be writing a draft at first and that this draft will then be polished into something suitable for publication. So, they say, I have my story idea, why can't I just start on the first draft? Why can't I just write "Chapter 1" at the top of the page and just start?
Well, you can try it if you like, but it will lead to a long hard road and that road will probably be one that will never end. The great majority who try this become so frustrated and so bogged down that they never make it to publication. Most, actually, don't write anything - except "Chapter 1".
Writing an outline is not the nasty chore that some assume it to be. Your Outline is the most helpful tool you will have. Writers write in different ways, but that aside, the great majority need some sort of outline as their guide. Even those who know a great deal of detail of what they want to be in their book from the beginning to the end, still find outlining their ideas an invaluable tool.
If an outline is done well, once you start your first draft you will be so grateful. Your outline can be used to keep you moving forward - momentum is important when you are writing.
An Outline is like a map. If you haven't got a map you are most likely to become lost. You will never get there if you don't know where you're going.