To evaluate success at Slack, I would concentrate on a mix of user-related, financial, and operational metrics, as they offer a comprehensive perspective on the organization's performance. Regarding user metrics, I believe that Daily Active Users (DAU), user growth rate, and user retention rates are strong indicators of success. Essentially, if users are regularly engaging with Slack and we continue to attract and keep more of them, we are successfully meeting their needs and demonstrating effective adoption. From a financial perspective, metrics such as revenue growth, profitability, and Average Revenue Per User (ARPU) can reflect how effectively we can monetize our user base and the efficiency of our business model. It is crucial that as we expand our user base, our financial metrics also show improvement to validate that the business is scalable. Lastly, operational metrics like application performance, uptime, and bug resolution times are vital for a software company. If Slack consistently operates smoothly with minimal bugs and high performance, it suggests that we are fulfilling user expectations, which can result in increased satisfaction, retention, and ultimately, success.