I made the mistake of doing am MS 150 ride with people from my work. A number of them thought that they would be fine even though they'd barely ridden, because they worked out in the gym.
They were so slow I couldn't stand it. After an hour, I ditched them, rode the century option, and got to the Hotel 3 hours before they finished the 75miles for the day. All but 2 abandoned before day 2, and none fininished.
People just don't understand that it takes some specific training, adaptation, and skill to ride a bike a substantial length.