unity IEnumerable works with 6 seconds but not with 7 seconds code example

Example: wait for seconds unity

//In the example below the script will right "Hello" and 3 seconds later write "Goodbye" in the console
Start()
{
  	//Call the function Example()
	StartCoroutine(Example());
}

Example()
{
  	Debug.Log("Hello");
  	//wait 3 seconds
	yield return new WaitForSeconds(3);
  	Debug.Log("Goodbye");
}