There’s a longstanding debate about whether even pacing in always best in long (i.e. more than about four minutes) races. Physiologically, it makes sense — but when you look at the actual pacing patterns of world records, they almost universally tend to form an inverted-U shape: slightly quicker start, steady in the middle, then speeding up again at the end.
I’m a fan of the fast start and fast finish.
A slow beginning, and a steady high pace after that, would make most sense physiologically, but we’re only human. So psychology plays a major role. In the beginning we think; “I can do this! If I show others how fast I am they will get demoralized and it will be over quicker!”. After 10 minutes you realize that you’re not there yet, and oh, it’s still a long way, better to conserve a bit of energy. Toward the end you can go for broke, collapsing at the finish for dramatic effect. We are not machines, we have no real idea, when we start, how our body will perform. In the begin of the race we’re optimistic, in the middle reality sets in, and towards the end we don’t give a damn. It’s like real life! Hence the inverted-U shape.