Incorrect lock usage - SynchronizationLockException guarantee

gistfile1.cs

class Program
{
    private static object locker = new object();
    
    static void Main(string[] args)
    {
        Monitor.Enter(locker);           
        Console.WriteLine("In Main Thread");
        ThreadPool.QueueUserWorkItem((o) => {
            Console.WriteLine("In New Thread");
            Monitor.Exit(locker);               

        });

        Console.ReadKey();
    }
}