extension methods - Casting and Linq Cast<T>() -

While trying to answer, I searched the following:

  string s = "Test"; Var result 1 = s.Select (c => (ushort) c); // work fine var result2 = s.Cast & lt; Ushort & gt; (); // An unlawful artist throws an exception  

Why Cast & lt; T & gt; () here fails? What is the difference?

Think you will find your answer here:

IEnumerable & LT; T & gt; . This means that every time from time to time every value is delivered to the point where it is being inserted, it already has System.Object