Once an athlete gets to a very high level, there is very little difference in time-related ability. They can all go out fast, kick, push the middle, etc. With all being even, athletes must gain an advantage. Leading and spending 2% to 4% more energy simply breaking still air (via physiology calculations)is an easy way to get beat. Rarely does one lead coast to coast for the win in a top competition. Johnny Gray could do this versus US guys but typically faltered at the world level when abilities were even. A good high schooler can do this until he/she faces competition that is equal in ability. This does not even take into account the increased relaxation of sitting in a pack like you are on an easy run until kicking time. So to answer the thread's question: "Leading will almost assure a runner will not win." That is why most top-level runners will not lead. They are not afraid, just smart. Rabbits are not solely to set a pace, but to aid the runners behind.