When you cycle you will know it, cycling changes your life.
Training for 100 k means just doing the thing you might not like but when you change clothes you become another person. Then you go for it. You just cycle 50 kilometer and 8 kilometer extra.
Those 8 kilometer extra makes you better.
It makes you feel you can handle the whole wide world.
But the same feeling count for running. For me running the marathon needs commitment to a certain life style. Eating and drinking has to be adjusted to the training schedule. In fact for people who run the marathon and work fulltime it's a hell of a job.
Tomorrow my colleague tries to run the 42 kilometer and 195 meter. I wonder what her time will be. She hopes to run it in 4 hours. My time on my first marathon was 3:54 hours. She can do that too.