Brilliance doesn’t significantly decrease the tendency to make mistakes, it just allows one a bigger scope of mistake-making. Combine that with the Peter Principle, and then truly brilliant people can make world-altering errors.
Also many brilliant people accustomed to succeeding often get the attitude that, “I’m really good, therefore anything I do is great, so unethical or illegal action X is also just fine due to the transitive property of my awesomeness.”
Not that I know anything about that personally.
No. That was, uh, about a friend. And stuff.