The key to owning a journal to me is that you give yourself leave to write whatever comes to mind.
Journaling can be revelatory, because the common-place seeming things you write one day can lead to insights into your deepest self on another day.
Further, journaling is an invaluable tool for charting your progress as a writer. Capturing the ideas, realizations, and false starts will prove useful to you and posterity, once you are the world-famous author you were meant to be.
Many greats have kept journals, but for all of those who did not....god damn! We wish you had! Imagine how much insight we would have into the process of the un-journaled greats if they had! A priceless contribution to the furthering of the ultimate artform, writing, for the betterment of humanity. So do it for your ancestors, if nothing else.