The voice is like a sonic fingerprint: the human voice is quite individual, and no matter what sound you make, it will always be uniquely yours. When you don’t worry about what it will sound like and just let your voice out, it is almost like letting your individuality and identity come out and imprint itself onto the world. There is a truth to this that is not only metaphorical: when you use your voice, the molecules of the air around you, the physical objects within earshot of your voice, do in fact vibrate in a unique pattern that is representative of your individual “voiceprint.”
In the arts, including visual art, music, and writing — and in the social world generally — we can talk about “finding one’s voice,” meaning discovering a way of expressing yourself that has nothing to do with being egotistical (or trying too hard to be zen-like and non-egotistical). I think it just means recognizing the aspects of your expression that an undeniable part of who you are, your mental and physical condition, your history and experiences that form who you are. This is how I understand “authenticity,” and it declares itself in the fact that we are all authentic beings in this universe.
Shintaido, however is not a martial art. You are not required to “keep your cool” at all times in Shintaido practice. There are parts of the practice, in fact, when the best thing you can do is “lose your cool,” let your hair down, look up at the sky (or imagine you have x-ray vision and can see the sky through whatever non-sky roof, ceiling, or other obstacle is above you), scream your lungs out, and let whatever feelings you have come out with no expectations of what they will be. If you feel shy, then “yell” quietly in a shy little voice. That’s you, too. Having no expectations about what will come out, I guarantee that whatever sonic expression comes out, it will be yours. You are a unique combination of flesh and blood, made from the dust of stars. Your body, your mind, everything around you, and everything you are capable of experiencing, every thought, every feeling, grows from the universe like apples grow from the branch of an apple tree. You are not an alien visiting “your life.” If you have feelings about that, using your voice can be a great way to ventilate them.
Sometimes it’s hard to imagine such mystical ideas like “let your inner light shine” or vague almost abstract “energies,” “qi / ki,” etc. But opening our mouths, letting the air flow out over the vocal chords, and making a vibration that is uniquely ours — most of us can do that.