如何正确地投射通过反射创建的对象

I'm trying to wrap my head around reflection, so I decided to add plugin capability to a program that I'm writing. The only way to understand a concept is to get your fingers dirty and write the code, so I went the route of creating a simple interface library consisting of the IPlugin and IHost interfaces, a plugin implementation library of classes that implement IPlugin, and a simple console project that instantiates the IHost implementation class that does simple work with the plugin objects. I'm trying to wrap my head around reflection, s