Example of why FxCop rule CA2214 (Do not call overridable methods in constructors) matters

CA2214Example.cs

class C : B
{
    string s;
    public C()
    {
        s = "hi";
    }
    protected override void F()
    {
        Console.WriteLine(s.Length); // NullReferenceException
    }
}
abstract class B
{
    protected B()
    {
        F();
    }
    protected abstract void F();
}