Why can I not assign a List of concrete types to a List of that concrete's interface?

Question

Why does this not compile?

public interface IConcrete { }

public class Concrete : IConcrete { }

public class Runner
{
    public static void Main()
    {
         


        

Answer 1

foreach (var item in myList)
    DoStuffWithInterface(item);

or

public void DoStuffWithInterface(IList concrete) { }

or

var myNewList = myList.Cast();