As you have already detected, there are many ways to write a book and every author brings something new to the process. If careening into an unknown future is a comfortable writing style for you, then best of luck in your endeavors.
"Just cause I don't know where I am going, doesn't mean that I am lost."
On the other hand, if you get weary of randomly rambling around in your fictional world, there are many, many other approaches which have worked for successful authors in the past. Be open to new experiences, including the to-you-heretical experience of planning ahead.