在for循环之前实例化和在for循环中实例化的区别

所以我刚刚开始学习c#，我遇到了这个练习，滚动一个骰子N次，然后打印每边滚动的次数。然而，我得到了答案，我的问题在于在循环之前和循环中实例化一个Random数字对象。

我的代码是这样的(这是循环之前的实例化):

static void DiceRoll(int RollTimes)
    {
        int roll = 0;
        int counter1 = 0;
        int counter2 = 0;
        int counter3 = 0;
        int counter4 = 0;
        int counter5 = 0;
        int counter6 = 0;
        Random rnd = new Random();
        for (int ctr = 0; ctr < RollTimes; ctr++)
        {
            roll = 0;
            roll = (int)rnd.Next(1, 7);
            switch (roll)
            {
                case 1:
                    counter1++;
                    break;
                case 2:
                    counter2++;
                    break;
                case 3:
                    counter3++;
                    break;
                case 4:
                    counter4++;
                    break;
                case 5:
                    counter5++;
                    break;
                case 6:
                    counter6++;
                    break;
            }
        }
        Console.WriteLine("1 is rolled {0} times.", counter1);
        Console.WriteLine("2 is rolled {0} times.", counter2);
        Console.WriteLine("3 is rolled {0} times.", counter3);
        Console.WriteLine("4 is rolled {0} times.", counter4);
        Console.WriteLine("5 is rolled {0} times.", counter5);
        Console.WriteLine("6 is rolled {0} times.", counter6);
    }

，结果如下:

1 is rolled A times.
2 is rolled B times.
3 is rolled C times.
4 is rolled D times.
5 is rolled E times.
6 is rolled F times.

在我做对之前，实例化行(Random rnd = new Random();)在循环中。

for (int ctr = 0; ctr < RollTimes; ctr++)
        {
            roll = 0;
            roll = (int)rnd.Next(1, 7);
            Random rnd = new Random();
            // rest of the code

则结果(随机):

1 is rolled (N) times.
2 is rolled (N) times.
3 is rolled (N) times.
4 is rolled (N) times.
5 is rolled (N) times.
6 is rolled (N) times.

谁能解释或启发我为什么实例化的位置会改变结果?谢谢!