Buffett gave us four investing criteria. The fourth one depends on a number nobody else can verify.

In his 1977 letter Buffett laid out what he wants in a business, and the wording is worth quoting exactly: "We want the business to be (1) one that we can understand, (2) with favorable long-term prospects, (3) operated by honest and competent people, and (4) available at a very attractive price." I keep coming back to that fourth one. After 12 years of investing I think it works differently from the other three, and it took me a while to see how. The first three you can reason your way toward. Understanding the business is just study. Favorable long-term prospects means a durable moat, and you can assess whether the high returns survive competition. Honest and competent management shows up in capital allocation and how they treat shareholders. Hard work, but two careful people looking at the same evidence usually land in roughly the same place. The fourth is different. And to be fair to Buffett, he did define it, more than people give him credit for. His answer is margin of safety: the gap between price and intrinsic value, with intrinsic value estimated through owner earnings discounted back. That is a real method. Far more rigorous than the P/E and P/B comparisons most people actually use. It is the core of what Graham taught him. The problem is that intrinsic value is not observable. It is an estimate, and it depends entirely on the assumptions you feed it. Two disciplined investors run owner earnings on the same company, pick slightly different growth and discount rates, and come out with fair values 40% apart. Both are following Buffett to the letter. Both have a margin of safety against their own number. And they completely disagree on whether to buy… That is the weak point. Margin of safety measures price against a number you made up yourself. It can't really be falsified, because if the stock drops you just say the market hasn't caught up to intrinsic value yet. The first three criteria anchor to the business. The fourth anchors to your own estimate, and you are the least objective thing in the room. The honest version of the fourth criterion has to anchor price to something outside your own head. And there is one number that fits: every market price already implies an expectation about future growth, and that implied number is the same for everyone looking at the stock. So instead of asking whether the price sits below my private estimate of value, the better question is whether the growth the price implies is something the business can actually deliver, given its returns on capital and how much it can reinvest. That comparison doesn t run through my assumptions. It compares two things anyone can check. That is the version of "attractive price" I think Buffett was approximating with judgment for decades without ever writing it down. Curious how people here actually judge it. Margin of safety on your own intrinsic value estimate is the standard answer, and it quietly leans on the one input nobody else can verify.