Margin of safety — the price you pay is the risk you take
The single most important question about an investment isn't "is this a good company?" — it's "am I paying meaningfully less than it's worth?" The gap between the two is the margin of safety, and it's what protects you when you turn out to be wrong, the world changes, or you were simply unlucky. A wonderful business bought at a punishing price is a poor investment; an ordinary business bought cheaply enough can be a fine one.
What it is
Margin of safety is the discount between a conservative estimate of what a business is worth and the price you actually pay. Buy a £1 of value for 60p and you have a 40p cushion — room for your estimate to be too optimistic, for a bad year, for a surprise, and still come out whole. The cushion is the whole point: you assume you'll be wrong some of the time, and you buy in a way that survives it.
Why it matters — price is risk
The common picture of risk is a wobbly share price. We think that's the wrong picture. The real risk is permanent loss of capital, and the biggest driver of permanent loss is the price you paid. Overpay for even a great business and a perfectly ordinary disappointment can take years to recover from; underpay and the same disappointment barely scratches you. So the price on the screen isn't just what you spend — it's how much risk you're absorbing. This is also why we treat a hard margin of safety as a pre-condition, not a nice-to-have: no amount of quality or confluence earns a position bought with no cushion.
How we use it
- We size so that no single position going to zero can be fatal. If the only way an idea works is for nothing to go wrong, it's too big.
- A margin of safety must be present before the conviction signals are even allowed to count — it's the floor, not a tie-breaker.
- It pairs with mean reversion to a quality-backed trend: the cushion is what lets you hold a cheap, genuinely good business through the wait for the price to find its long-run path, rather than being forced out at the worst moment.
The honest caveat
Cheap is not the same as a margin of safety. A falling price can mean the value is falling just as fast — a value trap, not a bargain. The cushion only exists if the value is real and durable; the discipline is estimating that value conservatively and honestly, then insisting on the discount anyway.
A plain-English explainer of how we think — part of our evidence-driven framework. Not investment advice.