Understanding AsyncFiberException in Effect Typescript

import { Effect, Layer, ManagedRuntime } from 'effect';

const runtime = ManagedRuntime.make(Layer.empty);

runtime.runFork(Effect.async(() => {}));

// AsyncFiberException: Fiber #3 cannot be resolved synchronously. This is caused by using runSync on an effect that performs async work
runtime.runSync(Effect.sync(() => {}));