An undependable vehicle is a hard sell on the car lot. "It works most of the time" won’t inspire a buyer to even kick a tire. Similarly, office leaders don’t like to hand off key assignments to someone who will probably be successful. They want as much of a guarantee as possible and a track record of proven success.
So be careful of what you promise. Give yourself a navigable path. Seek clarity on expectations and be clear about what you are able to do. Then go ahead and deliver consistently.