Sam Harris: Lying
Every lie haunts our future. There is no telling when or how it might collide with reality, requiring further maintenance.
Lies beget other lies. Unlike statements of fact, which require no further work on our part, lies must be continually protected from collisions with reality. When you tell the truth, you have nothing to keep track of. The world itself becomes your memory, and if questions arise, you can always point others back to it.
Honest people are a refuge: You know they mean what they say; you know they will not say one thing to your face and another behind your back; you know they will tell you when they think you have failed - and for this reason their praise cannot be mistaken for mere flattery.
Lies are the social equivalent of toxic waste - everyone is potentially harmed by their spread.