Even things like razor blades have imperfections if looked at closely enough. Crafters can only create things to appear perfect to a certain extent. Even when an object or art form seems consummate from afar, it most likely is ever so slightly imperfect or incomplete. For example, at first glance a solid object may cause the assumption that there are no flaws to it but, when a magnifying glass is held up to it there could be texture that was not intended to be seen. Slight imperfections can go unnoticed, complete perfection is close to impossible.
Wabi Sabi is not only applied to object but also to all forms of art. It can be practiced with paintings and sculptures along with singing and dance. There are plenty of examples of these art forms that could be described as imperfect, impermanent and incomplete. Abstract paintings that consist of different color splotches could be described as wabi sabi. A hand sculpted cup or bowl will inevitably have some disfigurement. This does not mean that wabi sabi art is ugly, to me it plainly means it is