Node.js achieves this through the use of an event loop. The event loop listens for events, such as the completion of an I/O operation, and then places the corresponding callback function on an event queue. The Node.js runtime processes the event queue in a single thread, ensuring that callbacks are executed in the order in which they were received. This allows the Node.js application to handle a large number of concurrent requests without being bogged down by the overhead of creating and managing multiple threads.