There's a whole bunch of things I don't know a thing about — I just stay away from those. So, I stay within what I call my circle of competence. - Warren Buffett

Investors should be skeptical of history-based models. Constructed by a nerdy-sounding priesthood using esoteric terms such as beta, gamma, sigma and the like, these models tend to look impressive. Too often, though, investors forget to examine the assumptions behind the models. Beware of geeks bearing formulas.

Risk comes from not knowing what you're doing. "The Three Essential Warren Buffett Quotes To Live By" forbes.com (20 April 2014)

The attitude of our managers vividly contrasts with that of the young man who married a tycoon's only child, a decidedly homely and dull lass. Relieved, the father called in his new son- in-law after the wedding and began to discuss the future:

Son, you're the boy I always wanted and never had. Here's a stock certificate for 50% of the company. You're my equal partner from now on.'

Thanks, dad.'

Now, what would you like to run? How about sales?'

I'm afraid I couldn't sell water to a man crawling in the Sahara.'

Well then, how about heading human relations?'

I really don't care for people.'

No problem, we have lots of other spots in the business. What would you like to do?'

Actually, nothing appeals to me. Why don't you just buy me out?