According to White House counsel Charles F. C. Ruff, Bill Clinton could not have perjured himself because "in his mind -- and that's the heart and soul of perjury -- he thought and he believed that what he was doing was being evasive but truthful."
In other words, if your view of reality is sufficiently distorted by self-interest, as Clinton's no doubt is, then you simply can't commit perjury. If you are sufficiently solipsistic, you are immune to prosecution for lying under oath.