If you have a more neutral color you probably won't need a mirror, just remember to use lip balm first. if it's a more saturated hue, use a mirror OR you can use the "selfie" mode on your phone camera to apply!
I got a nude ish color so it matches my lip well. This isn't an easy touch up product. It can stain your skin if you miss you lip. It also accentuates any dryness or flakiness in your lips so you want to look in the mirror to help that as well.