Your Body Temperature Is 98.6°F Everyone knows that. Except it’s not. In 1851, German physician Carl Wunderlich took a million temperature readings and calculated the average: **37°C**. Nice round number. Then someone converted it to Fahrenheit. 37 × 9/5 + 32 = 98.6 Suddenly a measurement rounded to the nearest whole degree became precise to the tenth of a degree. The conversion created precision that never existed in the original data. We’ve been teaching it ever since. Your pediatrician has it memorized. Your thermometer has a line at 98.6. The number feels scientific because it has a decimal point. Actual human body temperature? Probably closer to 98.2°F. And it varies throughout the day. But 98.6 stuck because precision signals certainty. Now look at your last investment memo. Purchase price: $8,450,000. Year 3 NOI: $891,456. Exit proceeds: $14,238,901. IRR: 17.34%. That IRR is your 98.6. Converted precision that never existed in the inputs. Your exit cap rate assumes stable interest rates. Your rent growth assumes no new supply. Your renovation budget assumes the contractor’s bid holds and you don’t find asbestos. Three shaky assumptions stacked together. Calculator spits out 17.34%. Not “high teens.” Not “15-20% depending on execution.” Exactly 17.34%. Real estate has tools to show uncertainty. Sensitivity tables. Best case, base case, worst case. Monte Carlo simulations. Then you write the pitch deck. The tables vanish. One number survives. Why? Because your LP expects 17.34%. Your loan committee built their model around it. Nobody wants to hear “high teens, depending.” So we manufacture certainty because admitting uncertainty costs us the deal. Precision transforms judgment into fact. “This deal might work” becomes “this deal returns 17.34%.” One sounds like opinion. The other sounds like physics. But your math isn’t the problem. Your assumptions are guesses in business suits. A 50-basis-point swing in exit cap rates moves your IRR by 300 basis points. Interest rates climb 1%? There goes 8 points of return. Rent growth off by 2%? The deal barely clears your hurdle. A surgeon needs to know the tumor measures 2.3 centimeters. The decimal point matters because the organ sits exactly where it sits. Your exit cap rate doesn’t sit anywhere. It’s wherever the market lands in five years. Driven by Fed policy you can’t predict, supply you can’t control, and buyer sentiment that might crater during the next credit crunch. The real skill isn’t calculating returns to two decimal places. It’s knowing which variables will kill you if they move 20%, then making sure you can survive when they do.​​​​​​​​​​​​​​​​