In a data-driven era, product managers often become enamored with metrics and dashboards, but not all metrics hold equal value for product growth. While some metrics offer genuine insights, others merely provide the illusion of progress, distracting from the true indicators of a product's health, such as retention, revenue, and user satisfaction. The key is distinguishing between signal metrics, which are resistant to manipulation and predictive of long-term success, and noise, which can obscure meaningful insights. The "one metric that matters" framework encourages focusing on a single, pivotal metric that aligns with customer value and predicts sustainable growth. Historical examples like Netflix and Apple illustrate that success often comes from observing user behavior and prioritizing what truly matters over superficial metrics. To find valuable metrics, product teams should anchor their measurements to user value, prioritize behavior over intent, seek out leading indicators of success, and regularly revise their metrics as the product evolves. Ultimately, the most impactful metrics are those that compound over time, driving meaningful product development and user engagement.