The Spontaneous Activity
For years I did activities with people, usually not as an organiser for one very simple reason. Micro-managers. These are the people that have an opinion, and a schedule, that want to take control of a simple activity. These people take a spontaneous activity and make it a nightmare.
For me the entire joy of going to do a hike, or a Via ferrata, or other things is to decide on a meeting place, and time, and do it.