Why C # Func <interface> lambda expression requires drop for result

Question

I need to understand an expression like Func deeper.

public class TheResult : IResultEntry { ... } 

With the above class, why does the second method require casting ?

I can read the error message, of course, but it's hard to understand.

 // Success public Task<IResultEntry> ProcessAsync_1() { return Task.Factory.StartNew(() => (IResultEntry) new TheResult()); } // Fail: Compiler error. Cannot implicitly convert... public Task<IResultEntry> ProcessAsync_2() { return Task.Factory.StartNew(() => new TheResult()); } 

If we change it to a named method using ReSharper, we can do without translation.

 public Task<IResultEntry> ProcessAsync_2_Changed() { return Task.Factory.StartNew(function); } private IResultEntry function() { return new TheResult(); }