Phase 1: "Ugh, why do I run"
This is the point at which you pretty much have to talk yourself into the first few steps. Maybe some runners out there get super excited and can't wait to start their l o n g r u n but well, that is not usually the case for me. Not only do I wonder why I run, I also wonder things like "why do I torture myself like this" and "how long is this going to take." You see, it's not that I actually hate running or don't know why I run. I just build so much hype during the week in anticipating my long run that I make it a bigger deal than it really is.
Phase 2: Accept it.
At around 30% completion of the run somehow you stop thinking about how long you'll be running and just accept that it's going to be a while. I usually begin to feel grateful that I'm not injured and try to think of other positive facts like "at least I don't have to run 50 miles today" or "at least I have awesome music I can listen to."
Phase 3: "I can do this all day long"
My favorite part of the run is just after the halfway mark where I start feeling somewhat accomplished and strong. My pace increases and I think "I could do this all day long" and for some reason start contemplating if I should run further than I originally planned. At this point I remember why I run and I'll usually dance a little to my music.
Phase 4: So close.
The best part of the run. With about 2-3 miles left I see the light at the end of the tunnel and my pace is still holding strong. Even though I'm feeling tired I know if I just hold on for a little while longer it'll all be worth it when I finish it and guess what? It always is.