The 2007 Dublin Marathon was my second attempt at a life-long goal of a four-hour marathon. Five years earlier, I failed in London by just 45 seconds.

For months I trained to a peak of fitness in the mountains of County Kerry. The weather on the day was perfect. My son—David—would run by my side. What could possibly go wrong?

The early miles of a mass marathon are a scrum. Imagine being on a packed London tube train at rush hour. Now imagine running at the same time. Amongst the sea of bobbing heads, one simply follows the runner in front with blind faith. So, I never saw the pavement edge that tripped me, sending me sprawling to the ground.

My shock was replaced with the fear of being stampeded by the tsunami of runners. Has anyone ever been trampled to death by marathon runners? Hands grabbed me and pulled me to my feet, thrusting me back into the conveyor belt of moving humanity. But I was broken—putting any weight on my left foot brought a lightning bolt of agony.

David helped me hop to a first-aid station where a cluster of eager volunteers diagnosed a sprained ankle and said my marathon was over. After a brief discussion, I convinced them I would continue whatever, so they might as well do some actual first aid on me. I left a few moments later with my ankle so heavily bandaged my trainer had to be held on with duct tape.

Since my ankle would not bend, my gait was awkward. Each footstep brought a stab of pain and a marathon contains many footsteps. Before long, my good leg also complained about the extra load.

By half-way, I was ready to pull out. Another 13 miles of this? No way. David said he would pull out with me. So, I wondered if I might manage just one more mile? Then one more. One more mile became my mantra. I was never going to finish, but I could do just one more mile.

At 24 miles, the route became packed with cheering crowds whose enthusiasm boosted me onwards. By now, my ankle was numb and I was sure my foot had died.

Needless to say, we did not finish in under four hours, but sometimes simply finishing is enough.