Building reliable services with unreliable dependencies involves preparing for potential failures by employing strategies like asynchronous communication, redundancy, and message queuing. Dependencies, which are external services providing additional functionality, can fail, causing services to wait indefinitely or crash. By using tools like Gremlin to simulate failures, developers can test their system's resilience and implement measures such as "fail fast" strategies, where unavailable dependencies are quickly detected and users are informed through fallback plans. Asynchronous communication, utilizing libraries like JavaScript's Promises, allows services to continue processing while waiting for responses, improving user experience. Redundancy involves creating replicas of services to ensure continued operation in case of failures, while message queues like RabbitMQ decouple services, allowing for scalable and asynchronous communication. Testing these setups through scenarios like Gremlin's blackhole experiment helps identify and mitigate potential disruptions, ensuring systems remain functional even when dependencies fail.