Never Get Too Hung Up On Mistakes.

If You Understood A Business Perfectly And The Future Of The Business, You Would Need Very Little In The Way Of A Margin Of Safety. So, The More Vulnerable The Business Is, Assuming You Still Want To Invest In It, The Larger Margin Of Safety You'd Need. If You're Driving A Truck Across A Bridge That Says It Holds 10,000 Pounds And You've Got A 9,800 Pound Vehicle, If The Bridge Is 6 Inches Above The Crevice It Covers, You May Feel Okay, But If It's Over The Grand Canyon, You May Feel You Want A Little Larger Margin Of Safety.

To Invest Successfully, You Need Not Understand Beta, Efficient Markets, Modern Portfolio Theory, Option Pricing Or Emerging Markets. You May, In Fact, Be Better Off Knowing Nothing Of These. That, Of Course, Is Not The Prevailing View At Most Business Schools, Whose Finance Curriculum Tends To Be Dominated By Such Subjects. In Our View, Though, Investment Students Need Only Two Well-taught Courses - How To Value A Business, And How To Think About Market Prices.

I Wouldn't Want To Manufacture Cigarettes. But If I Owned - We Do Own Costco. Do They Sell Them? Yes. So I Don't Have A Problem Owning Stock In That. But I Just Wouldn't Want To - I Wouldn't Want To Do It Myself. I Basically Think, If Anything Is Sufficiently Antisocial, Society Should Do Something About It. But That's A Separate Question. But - And I Don't Think There's Any Company That I Have Seen That's 100 Percent Pure.

There Is No Perfect Mathematical Formula For Pricing A Business.

It Irritates The Hell Out Of Me But You Can't Buy Love.