Untitled

Why does this C# ThreadPool sometimes drop work items?
class Program
{
    private int x = 0;
    static void Main(string[] args)
    {

        Program p = new Program();
        int a, b;
        ThreadPool.GetMaxThreads(out a, out b);
        Console.WriteLine("{0} - {1}", a, b);
        for (int y = 0; y < 20; y++)
        {
            WaitCallback cb = new WaitCallback(DoSomething);

            ThreadPool.QueueUserWorkItem(cb, y);
        }
    }

    public static void DoSomething(object state)
    {
        Console.WriteLine(state);
    }
}