Why do I keep seeing small black hair pieces in front of my eyes?

Vitreous floaters. The hairs or lines are due to the shadow in your vision of a vitreous floater inside the eye in the vitreous jelly. They generally cause no harm but are annoying. In rare situations they can be a warning sign of a much more serious problem such as a retinal hole or tear. See your eye md if there is a large increase in the number of floaters that you see.