Im a 10K runner who for various reasons only had six weeks to train for the marathon. I set off at three-hour pace - silly I know, but I felt I could do it.
At 10K I felt great.
At 20K I felt good and still strong, albeit starting to work a bit harder.
At 30K I was getting stings of brief cramp.
At 32K I died.
I shuffled my way to the finish line in 3:30.