This shortest expression of who you are at your essence is meant to get to the most important part of your life experience so far. Think of what most defines who you are and what has given your life purpose or direction. If it helps to start off with a list first, jot down three of the most important themes or threads in your life, then select one of those to stay with. Think this through for as long you need to.
A way to approach this would be to think of the story you want to tell (even in 10 words) as your deepest life meaning, and how this would be told within the framework or pattern that all good stories follow: beginning, muddle, and resolution.
What you settle on could well end up being written as a long meaningful story, but keep this version to 10 words, because you’ll have time to flesh it out later. For now, distill what you come up with down to the most critical 10 words. It could be one sentence, two, or even three short, pithy sentences, or maybe a series of phrases. Go with whatever format, including verse, that makes the most sense to you. Which 10 words most characterize, capture, or clarify your life and who you are?