The doubter seeks sadistic pleasure in not letting you succeed particularly when times are tough and challenges are unknown. Your success means the doubter's failure.
You can't do it ... this task has never been accomplished ever before ... this is a new situation and you are not equipped with new world skill sets...the cost of failure is disaster.... you will be ridiculed and ostracized if you fail. A hundred such propositions will be put before you to make you drive in reverse gear. The doubter literally whispers to the warrior ... "You cannot withstand the storm"
But the strong and the believer is self confirmed to turn around and tell the doubter : "... until now I was only a storm chaser. Now , I am the storm !"
In moments of challenging situations, learn to be the storm !