I'm sensing a cycle here.
Today was supposed to be a 20-mile day. I've taken the entire week off, so the last time I ran was last Sunday, for 13 miles. I did that, but it hurt my left knee. Hence, week off. Yesterday I did the scheduled five miles at race pace, successfully, without my knee bothering me too much. But I could tell it hurt more today when I got up. I had a huge dinner last night in preparation, and my normal long-run breakfast, and I went about my business as if I were about to run 20 miles. Warmed up, hit the street, started running and made it about 200 feet before I quit. I just knew that even if I could make the whole distance, which I doubt I could have, my knee would have been back where it was a week or two ago if not much worse.
I'm trying really hard not to let this get me down, with varying degrees of success as the day wears on. I came home and worked out, because I'll be damned if I'm going to just sit on the at least 1500 calories I've taken in since last night. I think that helped me from falling into too much of an emotional hole, and writing this is helping too. But considering how much time I've put into this, and how close the marathon is, and how unsure I am as to whether I'll even be able to run it, it's hard not to get frustrated right now. I don't have much else going on right now, so if I lose this then I'm going to have a hard time.
Maybe I'll just write a novel instead.