I'm in training for my 5th marathon right now. Having done 4 already, I know the training, I know the gear, the nutrition, the need for BodyGlide, good socks, GUs/sport beans/Clif Bloks, etc.
But this is the first of my marathons where I've kept up decent mileage in the off-season. This is the first of my marathons where I'm physically fit enough to realistically and logically train for a marathon. This is the first of my marathons where I'm actually running most of my scheduled runs.
So why am I so nervous?
I figured out that I'm scared of what it means for me on race day. It means that I'm actually going to have to "bring it" mentally and that I'm going to have to push through my fatigue because I've trained to do so. In years past, if I was tired, I dropped to a walk and stayed there because it was comfortable and because I knew my half-assed training hadn't prepared me to go the full 26.2 running so why even try to make it past 20 running - hey, as long as I made it across the finish line, that was ok.
Now, I'm really training and that means no excuses on race day. Damn, that's scary.