As a CEO with a tech background and venture capitalist, the key metric I prioritize is 'retention rate'. For me, it's a litmus test of how much value the startup delivers to its customers. If a product or service keeps users coming back, it's usually a sign of excellent value proposition and customer satisfaction. However, if users churn rapidly, it's a red flag. It potentially signals deeper issues either with the product or the market. Therefore, a high retention rate indicates a stronger potential for growth.