I think running for yourself is something like a meditation, you have your speed and your goal and just go ahead. Running in such a group is very distractible, because in such marathon that is going to happen in our area, everyone is welcome, that means people may even not to be runners and just took part for charity. It is noticeable how the runners at the beginning are concentrated, they do not pay attention to anyone and just run with their one pace quite distanced from others. That deserves all respect. The same time you can see that those who are in front of the crowd have a good gap from the rest and maybe that is also helpful for them to do what they like to do :)