Reading your own writing is a little bit like looking at yourself in a photograph or video. It provides you with an opportunity to see yourself from across the room. It's not the same as seeing yourself objectively or seeing yourself as someone else sees you: other people have preoccupations of their own. They often do not notice the things that jump off the screen at you because they are not self-conscious about the way you look or sound. You are likely to be self-conscious.
If you read something you wrote some time ago, you will notice that paradox of the human self: you are aware of both being the person who wrote what you just read and of no longer being the person who wrote it. You can notice change in yourself - you notice that you have said things in words or phrases that no longer come naturally to you. You can notice that the way you organize your thoughts has changed. You can notice that the things you wrote seemed inevitable at the time, and now seem subject to change.
When you are lucky, you read something you wrote and you respond as you would to a younger friend, noticing beauty or enthusiasm or strength or clarity. When you are lucky, you think: I remember being the person who wrote this, and I notice now that I was stronger or smarter or more creative than I thought I was.
When life happens differently, you look back and squirm a little. Did I really think that was something I should put into words? What was I thinking?
Writing lasts a long time. When you write, consider the people for whom you are writing. Then consider that reader who, in a few weeks or months or years, will be you - and write something that will make that person smile.