The investor's concept of a margin of safety

 The investor's concept of a margin of safety rests upon a simple and definite arithmetical reasoning from statistical data.

1. There is no guarantee that the fundamental quantitative approach will be successful in the future, but no reason for pessimism. 
2. "To have a true investment there must be present a true margin of safety." 

"It is our argument that a sufficiently low price can turn a security of mediocre quality into a sound investment opportunity--provided

• that the buyer is informed and experienced and 
• that he practices adequate diversification. 

For if the price is low enough to create a substantial margin of safety, the security thereby meets our criterion of investment.


http://www.conscious-investor.com/books/intelligentinvestor.pdf