Vulnerability. Great storytellers really never tell about triumphs — they always focus on weakness and loss, and their own humanity, their own clownishness. So, anytime a storyteller really opens up and is really vulnerable, the audience immediately responds.
Here's an animation of Ira Glass talking about taste, the challenges beginners face, and why they need to do a lot of work:
Ira Glass offers tips on storytelling that apply to comedy too [Sandpaper Suit]
5 Tips for Telling Better Stories [NY Times]