if only we could ignore those thoughts in our head, on demand.
from my experience, the more I think about a potential run, the higher the chance that i'll break down mentally. don't get discouraged with any of the 'self doubt' thoughts, everyone gets them.. I don't think they ever really go away tbh... the thing that makes it sweet is finally achieving some goal in the midst of training where your brain is constantly telling you to stop. Your brain just wants you to stop & get on the couch and eat funyuns. our brains are weak bichez.
as for the negative thoughts.. no matter what pace i'm running, they always happen when I START running.. ie the first minute or so. After that, if i'm not pushing myself to the extreme, they start to go away. If i'm pushing myself to the max, they are there for most of the run.. so I think your brain telling you to stop when you first start running, is pretty normal.
some elite ultra-marathonner, navy seal guy once said something interesting.. on an ultra run, he just keeps telling himself stuff like: "just run 10 more feet hard" .. then when he runs those 10 feet, he says it again.. and again.. and again.. lmao.
edit: David Goggins
http://www.adarq.org/800m-running-andor-conditioning/david-goggins-ultra-endurance-athlete/msg120495/#msg120495you'd like this guy.. i recall maybe having talked about him before with you, dno. Anyway check that first video.