Walking past the beautiful Bank of England building one day, I was reminded of a curious principle named after Charles Goodhart, a former advisor to the Bank of England. In 1975, he formulated a rule now known as Goodhart's Law: "Any observed statistical regularity tends to break down once pressure is applied to it for control purposes." In essence, when we set a target to achieve a certain metric, the old patterns that once made that metric meaningful stop working. Simply put, "when a measure becomes a target, it ceases to be a good measure." ✅Epigenetic age: When we replace hard endpoints in research with biomarkers, we risk making critical errors. For example, epigenetic age can be reduced by taking vitamin D, growth hormone, folate (B9), B12, and consuming certain foods (like poultry). However, none of these interventions reduce mortality or extend lifespan. ✅The Vitamin D paradox: High levels of vitamin D in the blood are strongly linked to lower risks of various diseases—cancer, autoimmune disorders, obesity, and diabetes—according to numerous studies. The quality of this research is beyond doubt. However, taking vitamin D supplements above normal levels proves almost useless. Why? Vitamin D levels are a reflection of how much time someone spends outdoors, which correlates with being more physically active, socially engaged, and overall healthier (versus being stuck indoors). Plus, there are other compounds produced under sunlight that supplements can't replace (more than a dozen, from nitric oxide to proopiomelanocortin). This doesn’t just apply to vitamin D, but to many other markers, from homocysteine to zinc. ✅Weight loss. Many people make weight reduction their primary goal, tracking progress solely by the number on the scale. This often leads to unhealthy practices like extreme diets or loss of muscle mass instead of fat. In the end, the pursuit of their goal leads to burnout and eventual weight gain. The more they lose, the closer they get to failure. It’s like trying to evaluate a car’s condition based solely on mileage (which can easily be tampered with), assessing love by the number of gifts exchanged, or judging children based on their grades. Goodhart’s Law applies to society as well. If businesses are rewarded based on the weight of their production, products become heavier. If transportation companies are judged by kilometers traveled, routes become more complicated. If education is measured by test scores, the entire system bends toward teaching to the test. 😬When company rankings or performance metrics become the focus, efforts shift toward manipulating those numbers at any cost. In some cases, countries—like Belarus—falsify economic data or infant mortality rates just to climb higher in UN rankings. The same is true for academic metrics: when citations become the benchmark, the quality of research declines, and the number of low-quality papers skyrockets. Metrics are useful, but they should guide us, not be our ultimate goals. It's always important to focus on real, meaningful outcomes. When setting goals or evaluating progress, it's crucial to keep Goodhart’s Law in mind, so we don’t lose sight of what really matters.