Here’s an interesting read for anyone who has ever trained for and runs marathons. There’s a lot of variables that go into running. Just when you think you’ve got it and you’re ready, you show up on race day and run your worst time. Trust me, it happens.
After training for four months (and preparing all year), I lined up last weekend at the start of an unseasonably warm Marine Corps Marathon, went out strong and well paced, and somewhere in the second half completely fell apart. Whatever the opposite of a PR is, that’s what I earned. It was my Personal Worst. I came in 45 minutes slower than my goal time, and nearly 30 minutes slower than any marathon I’ve ever run before. What happened? I wasn’t being realistic.
Source: What Happens If You Train All Year for a Marathon, and Fail Miserably? | Runner’s World