Clarify middleware ordering (dotnet#5802)

aspnetcore/fundamentals/startup.md

@@ -71,11 +71,13 @@ The [ASP.NET Core templates](/dotnet/core/tools/dotnet-new) configure the pipeli
 
 [!code-csharp[](../common/samples/WebApplication1DotNetCore2.0App/Startup.cs?range=28-48&highlight=5,6,10,13,15)]
 
-Each `Use` extension method adds a middleware component to the request pipeline. For instance, the `UseMvc` extension method adds the [routing middleware](xref:fundamentals/routing) to the request pipeline and configures [MVC](xref:mvc/overview) as the default handler.
+Each `Use` extension method adds a middleware component to the request pipeline. For instance, the `UseMvc` extension method adds the [Routing Middleware](xref:fundamentals/routing) to the request pipeline and configures [MVC](xref:mvc/overview) as the default handler. 
+
+Each middleware component in the request pipeline is responsible for invoking the next component in the pipeline or short-circuiting the chain, if appropriate. If short-circuiting doesn't occur along the middleware chain, each middleware has a second chance to process the request before it's sent to the client.
 
 Additional services, such as `IHostingEnvironment` and `ILoggerFactory`, may also be specified in the method signature. When specified, additional services are injected if they're available.
 
-For more information on how to use `IApplicationBuilder`, see [Middleware](xref:fundamentals/middleware/index).
+For more information on how to use `IApplicationBuilder` and the order of middleware processing, see [Middleware](xref:fundamentals/middleware/index).
 
 ## Convenience methods