Which of the following metrics is crucial for determining a startup's viability?

Customer retention rates are a critical metric for assessing a startup's viability because they provide insight into how well the company is meeting the needs of its customers and maintaining their loyalty. High customer retention indicates that customers find value in the product or service offered, suggesting that the startup has a strong market fit. This is essential for sustainable revenue generation, as retaining existing customers is generally more cost-effective than acquiring new ones.

Moreover, strong retention rates can lead to positive word-of-mouth, repeat purchases, and customer referrals, all of which are vital for a startup looking to grow and scale. In contrast, other metrics, such as employee satisfaction ratings, while important for internal culture, do not directly reflect market performance. The number of historical shareholders may provide some context regarding the startup’s funding history, but it does not indicate current operational success. Time to reach break-even can show financial efficiency but does not speak to ongoing customer engagement, which is often crucial for long-term success. Thus, customer retention rates offer a clear indication of a startup's ability to thrive in a competitive environment.