Are PB's a matter of luck? I mean (as Sally Gunnell would say), we all have good and bad days. Sometimes, infact, most of the time, no matter how hard you try, your run/race can be a total flop, even though you've trained your rear end off, eaten properly etc... Only to run like a donkey on the day!
The polar opposite can also be true though. last year I spent a week drinking and eating up to three days before the National 10k and managed to get a PB!
How do you regulate the quality of your racing? Was my performance enhanced by relaxation the week before, or was it the diesel like Spanish brandy I was consuming by the gallon?