There will come a point where your web application doesn’t behave the way you expect. Some problems manifest themselves in an obvious way—such as unexpected HTML content—and you need to figure out what goes wrong. Other problems are more complex and insubstantial, and you may have to dig deep into the application just to figure out what’s happening, let alone apply a fix.
The Visual Studio debugger is useful for finding the first kind of problem, which is usually caused by the way that single requests are processed. The other kind—the more elusive problem—is often caused by interactions between requests, or deep configuration ...