Doubt is an inevitable part of life.
These things may give us reason to say “no”– to back down or step away.  But they are so much more.They are the sign of an opportunity with which we would not generally be presented.  They are the gateways to something greater, that often leave marks behind (Yes, sometimes these marks are scars, but they can also be something beautiful).
So don’t take doubt as a warning sign you must heed.
Take it as a possibility to adventure.