Don't we wonder this, sometimes, as we sit alone writing? Yet when writing for publication we have an audience in mind.
When I journal, though, I am my own audience. It is a way to rejuvenate and grow. Sometimes I use the "word jar" technique. That is, select from your mind, or from any book, perhaps 20-30 interesting words, write them on slips of paper, and draw five with which to work. Or have a friend create a list for you. This gives an element of surprise to the writing that may trigger interesting insights. For this particular exercise, all five words are to be used in an opening sentence, and the writing proceeds from there.
Here's my most recent one:
Be a wellspring of cheerful, glowing strength, stirred by your passion for peace. Stand in your place, wherever it is. If you're made to be the baby of the family, be full of wide-eyed innocence, eager to absorb your elder's wisdom, for thus you bless them. If you're made to be the matriarch, be wise and generous in your place of power, and draw on all those around you for their insights for thus you are truly wise. If you're allowed to be a friend, listen carefully, question gently, be full of empathy and compassion. If you're made to be an enemy, stand firm where you must but as respectfully as you can, for you know that the compost becomes the flower and the flower becomes the compost, and the process is always ongoing. Anyone's understanding and position can change. The peaceful heart remembers this and draws forth new flowers again and again, thus creating a haven in this stormy world.