Not at all limited to law - accepting facts/stories/statements that fit one's worldview or even just seem interesting or important, and passing them on without ever checking or even doubting their correctness is a mistake that I see very frequently (and occasionally in myself despite conscious efforts to avoid it).
The young gun who assumes he understands architectural concepts without reading up on them, and re-invents the wheel (often producing a wheel that's tough to turn).
Then there's the cocky senior who doesn't need the latest and greatest because he already "knows" they do the same thing as his solution from 15 years ago (and when he's fired he can't find work because he's a dinosaur).
I know, I've been guilty of both :D
Edit : Come to think of it, the worst offenders are buzzword spewing managers and sales guys. "Oh the Cloud? Our product can mesh your business objectives with transparent synergies through the Cloud! Trust me, I'm an expert! Ah-hah-hah-haa"
