Web apps (well, well-functioning ones, anyway) helped this click for me. While the request is happening, there is state that is passed around, and contexts like

Web apps (well, well-functioning ones, anyway) helped this click for me. While the request is happening, there is state that is passed around, and contexts like the request, the user, etc.. and depending on what you're doing, you may be adding to that state, or modifying it, or whatever. But that state shouldn't persist beyond the request, otherwise you have problems. You shouldn't have one request modifying the state of other running requests, etc..