When you carry on a conversation in person, you don't have the opportunity to go back in time and change what you said 5 minutes ago. You retract it or correct it or apologize for it or add something to it in the present time. So think what you're writing the first time, preview it if that helps or read it immediately while still time to edit. Then if later you don't like it, post again to say so. If it's something you were wrong on then accept getting beaten up a bit and correct as the thread or conversation continues.