Lying vs. Bullshitting
Even though the two words at first glance appear to have similar meanings, there are fundamental differences between lying and bullshitting.
As the purpose and meaning behind lying consists of hiding the truth, one has to necessarily be both consciously aware of the truth and consciously attempt to keep it away from the person being lied to - lying, therefore, is an act intimately related to the veracity of the content being transmitted.
On the other hand, bullshitting (AKA talking out of one's ass, etc) is completely truth-ignostic. In order to bullshit, you don't have to know what's true and what isn't, and by definition the bullshitter doesn't even care whether or not what he's saying is true or not, even if the bullshitter knew. Bullshitting becomes an act of persuasion, meant to convince the receiver of the message about the contents of said bullshit: Truth becomes irrelevant, as it's not being actively pursued - neither to tell the truth to the receiver nor trying to hide it from him. What's important is how well the receiver buys into the bullshit instead of being successfully kept in the dark about the truth.
The word “bullshit” (or just “bull”) implies insincerity, a bunch of argumentative hot air: it's an act of casual argumentation, a sort of discursive bluff that, for some, even escapes conscious planning. Perhaps that's why there aren't a lot of people who lie because they enjoy lying (and those who do are instantly labeled as mythomaniacs, deemed to be pathological behavior), but conversely there's a lot of bullshitters out there who seem to do it as a hobby: the charm of argumentation and debate, even if insincere, doesn't seem to have lost any strength over all these centuries.