“To thine own self be true” – it’s an admonition and affirmation generally held in high regard, but it’s also one that can be difficult to live up to. In many instances, that’s attributable to not really knowing oneself in the first place. And, as this telling documentary from writer-director Andres Veiel reveals, that was very much the case where German filmmaker Leni Riefenstahl (1902-2003) was concerned.