Monolith to Microservices: When to make the leap?

Many of us have been through the journey of scaling a startup from a single server to a distributed cloud system. One of the most debated transitions is moving from a monolithic architecture to microservices. While the benefits of microservices - independent deployment, technology diversity, and improved fault isolation - are clear in theory, the operational overhead, increased complexity in data consistency, and the learning curve for teams can be substantial. I'm curious about real-world experiences: at what point in a company's growth did you find the move to microservices truly justified? Were there specific pain points that made the monolithic architecture untenable, or was it a proactive decision based on anticipated future scale? What were the biggest unexpected challenges during this transition?