Stars and companies fall from grace. Because of the public hanging, the fall is never pretty. And it’s far easier to explain what happened in hindsight than predict with foresight. Still, looking backward is how we learn our lessons. So here’s my take on NBC’s shocking change in fortune. Breaking your brand promise destroys trust. News anchors must convey the objectivity, rationality, and truthfulness their viewers demand. CBS’s Walter Cronkite is the gold standard. When your chief newsman appears on late night shows and tries to be funny or raises his hand to be Jay Leno’s replacement—as Williams did—you have a potential branding issue to manage proactively. Restlessness places brand promises at risk. Restlessness emerges when the status quo produces a feeling or reality of stagnation. John Stewart is exiting the Daily Show as he felt his viewers did not deserve a host…