Infallible

Infallible: Incapable of falling.

People who are filled with truthiness are bouyed by it and therefore never fall down. This was demonstrated by Stephen Colbert, the most infallible man alive, when he jumped into the mosh-pit audience at the Colbert Report for a bit of crowd surfing. Not only did he not fall, but his impeccably pressed suit was unaffected.

It just so happens that those who can't fall down also cannot tell a lie. This is a natural side-effect of extreme truthiness.