Unity3D C# 这个协程为何是死循环？

Question

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
    bool a = true;
    bool b = true;

    void Update()
    {
        if (a)
        {
            a = false;
            for (int i = 0; i < 3; i++)
            {
                if (b)
                {
                    b = false;
                    StartCoroutine("Wait");
                    Invoke("Stop", 5);
                }
                else
                {
                    i--;
                }
            }
            a = true;
        }
    }

    IEnumerator Wait()
    {
        int i = 0;
        while (i<5)
        {
            yield return new WaitForSeconds(1);
            i++;
            Debug.Log(i);
        }
    }

    void Stop()
    {
        StopCoroutine("Wait");
        b = true;
    }
}