Conditional variable is stuck on waiting

Why the condition variable is stuck on waiting if it was notified in worker_thread? What am I missing here?

std::mutex m;
std::condition_variable cv;

void worker_thread()
{
    cv.notify_one();
}

int main()
{
    std::thread worker(worker_thread);

    std::cout << "Start waiting..." << std::endl;
    std::unique_lock<std::mutex> lk(m);
    cv.wait(lk);
    std::cout << "Finished waiting..." << std::endl;

    worker.join();

    getchar();
}