If you could determine the one bit of running advice dispensed and received more often than any other, it would probably be 'Go out slow.' It would also be the one bit of running advice most frequently ignored. But it seems as though everyone—no matter their experience level—has recurring bouts of going out too fast and then struggling at the end. Mathematically it doesn't matter if you run the first half of a 10k in 20 minutes and the second half in 25 minutes, or vice versa, but I guarantee it will feel a lot different. It's reasonably well-established that for distances greater than 5k, you will average a better speed over the course of a race if you start more slowly than your goal pace, and gradually build up to it. The problem is our bodies naturally want to go faster while we feel fresh and slower when we feel tired. It takes some mental discipline to overrule our physical tendencies. Resist the urge to bask in how great you feel at the start of a race and how effortless it all is. Instead, remember your last gasping, stumbling finish. Once you experience the thrill of passing mobs of burnt-out bonkers in the latter miles, you won't want to go back.