Ok. Asset is parent of Stock: // upcast Stock msft = new

Question

Ok. Asset is parent of Stock: // upcast Stock msft = new

Stock();
Asset a = msft; // upcast

Console.WriteLine(a == msft);

Console.WriteLine(a.Name);
Console.WriteLine();

// downcast
Stock s = (Stock)a; // downcast
Console.WriteLine(s == msft);
Console.WriteLine(a == msft);
Console.WriteLine(s.SharesOwned);

why after downcasting a which is parent object, I cannot access child's property? I mean why I cannot use a.ShareOwned? SharesOwned is child's property