Margin of Safety, in plain English
Seth Klarman’s 1991 book is the most sought-after book in value investing. It has been out of print for decades, and used copies sell for many times their original price. Here are its main ideas in our own words, with six questions to ask before you buy anything.
Who Klarman is
Seth Klarman has run the Baupost Group in Boston since 1982, and it is now one of the largest hedge funds in the world. He is famously private: Baupost’s letters go only to its investors, and he rarely speaks in public. That makes the book, and his occasional talks, the best way to understand how he thinks.
1. Where most investors go wrong
Klarman starts by separating investors from speculators. An investor buys a share as a piece of a business and cares what that business is worth. A speculator buys because he expects the price to rise, whatever the business is worth. Most people who think they are investing are speculating.
He then explains why Wall Street works against you. Brokers and banks earn fees on activity and new issues, so they are paid to be optimistic and to keep you trading. And professional fund managers are judged against an index every quarter, so they are pushed to own what everyone else owns and avoid looking different, even when looking different is the only way to do well. He calls this a race the client always loses.
2. Avoid losing money first
The heart of the book is that the first goal is not to lose money. Klarman cares about absolute returns, not beating an index: being down 20% when the market is down 30% is still losing 20%. Because losses compound so badly (a 50% fall needs a 100% gain to get back to where you were), protecting the downside does more for long-term returns than chasing the upside.
That changes what risk means. To Klarman, risk is the chance and size of a permanent loss, not how much a price jumps around. A share that has halved for no good reason can be less risky than before, because you are paying less for the same business.
3. The margin of safety
Valuing a business is imprecise and the future is uncertain, so you will be wrong some of the time. The answer is to buy only when the price is well below a cautious estimate of what the business is worth. That gap, Benjamin Graham’s margin of safety, absorbs your mistakes and bad luck. It is also where the return comes from: when the price moves up towards the value, you make money without needing anything to go especially right.
Klarman stresses that value is a range, not a single number, and that it changes as the business and the world change. The market price, meanwhile, swings with fear and greed. Like Graham’s Mr Market, it is there to serve you, not to tell you what something is worth.
4. How to value a business
Klarman uses three approaches, and prefers to check one against another:
- The cash it will produce. Estimate the cash the business will generate and what that is worth today. He warns how sensitive this is to small changes in growth and discount rates, so assumptions should be cautious.
- What it would fetch if sold or wound up. What the assets would raise if the business were broken up or closed. This gives a floor, especially for asset-heavy or struggling companies.
- What the market pays for similar businesses. Useful as a check, but only as good as the prices it is based on, which may themselves be too high.
If none of the three gives a clear answer, he moves on. There is no shortage of things to look at, and an investor is never forced to have an opinion on everything.
5. Where bargains come from
Cheap shares usually have a reason to be cheap, and the best reasons have nothing to do with the business itself. Klarman looks where other investors are forced, bored or put off:
- Forced sellers, such as index funds dropping a company, or institutions that must sell a share after a rating cut or a spin-off.
- Spin-offs, where shareholders of the parent receive shares in a business they never chose and often sell them without looking.
- Complexity: unusual securities, messy structures and situations that take real work to understand.
- Distress and bankruptcy, where many holders are not allowed, or don’t want, to own a troubled company’s debt or shares.
- Catastrophes, when bad news about a sector or a market makes people sell the good with the bad.
He likes a catalyst too: an event, such as a sale of the company, a break-up, a buyback or a return of cash, that will close the gap between price and value rather than waiting for other investors to notice.
6. Running the portfolio
- Hold cash when nothing is cheap. Cash is not a failure; it is the option to buy later at better prices. Baupost has often held a lot of it.
- Buy in stages. Nobody catches the bottom, so start with part of a position and add if the price falls and your view of the value holds.
- Sell when the bargain has gone, not after a set time. When the price reaches your estimate of value, the margin of safety has been used up.
- Know enough to diversify sensibly. Own enough different positions that one mistake can’t sink you, but not so many that you don’t understand what you own.
- Think about liquidity. Be paid for owning things that are hard to sell, and don’t rely on being able to sell in a hurry.
Six questions to ask before you buy
- What could I lose, and how likely is it? Start with the downside. If the bad case would cost you a lot of money for good, the upside doesn’t matter much.
- What is the business worth, as a range? Value it more than one way, with cautious assumptions, and write down a low and a high figure rather than one number.
- How big is the discount? Only buy well below the low end of your range. The gap is your protection against the mistakes you will make.
- Why is it cheap? Name the reason: a forced seller, an unloved spin-off, a complicated structure, a bad year. ‘The market is wrong’ isn’t a reason.
- What will close the gap? A catalyst such as a sale, a buyback, a break-up or a return of cash helps, because cheap can stay cheap for a long time.
- What would I do if it halved? If your view of the value hasn’t changed, a lower price is a better bargain. Decide now whether you would buy more.
Hear it from Klarman
He rarely gives interviews, but a few recent ones are public. They are on his people page and in the video library, including a 2026 interview on AI and market bubbles. When he speaks again, sign up for alerts and we’ll email you.
You can also see what Baupost owns: its latest 13F shows the US shares it held at the last quarter end, how the portfolio has changed, and which other value investors own the same companies.
Reading the book
Margin of Safety: Risk-Averse Value Investing Strategies for the Thoughtful Investor (HarperCollins, 1991) is out of print, so new copies are rare and used ones are expensive. Check your local library first; some lend it, and library services can often get a copy from another branch.