margin of safety

A frequently asked question on value investing and how to calculate intrinsic value is this: how can you be so sure that the co's intrinsic value is this and at this price it is a good investment?

For those not so sure what the hell is going on, read these first
Value Investing
Intrinsic Value
Good Investment

Well, the truth is, you are never sure, you can spend 20 days calculating the intrinsic value of the company and become so sure that the stock is undervalued. So you buy and the stock tank 20%. Shiok huh?Intrinsic value goes hand in hand with margin of safety. Bcos you can never be sure whether you really got the intrinsic value right, you need to have a margin of safety. ie you will only buy the stock if the current price is way, way, WAY below your calculated intrinsic value.
As a rule of thumb, I recommend 40-50% below your calculated intrinsic value.Buffett used the example of building a bridge. If you know that the maximum weight of vehicles that will cross the bridge is 10 tons (based on historical statistics), will you build a bridge that will support 10 tons or a bridge that will support 30 tons?That is margin of safety.

Ben Graham, the grandfather of value investing once said this: if you need to surmise value investing into only 3 words, it would be "margin of safety". It is THAT important.Unfortunately, most investors don't really have this concept in mind. Even those who are very experienced. I guess it's not easy partly bcos have a strict margin of safety rule forces you to pass on many investment ideas even if they are quite good. And when you see them rally 100% after you decided NOT to buy them, wah shiok right?
Now every wall you see has a purpose. For you to bang your head hard on it! Haha!But having a margin of safety will make very sure that you will not lose your shirt. Even if you are damn wrong on your intrinsic value, you may lose a bit of money, the stock may tank 20%, but it won't tank like 80% and chances are after it tank 20% it will creep back up again, it will not bankrupt you. That's the strength if you have a huge margin of safety.