As chancellor of the University of North Carolina at Chapel Hill, on any given day Kevin M. Guskiewicz was reporting to at least a dozen important constituencies on campus. He used to tell people if he could keep 70 percent of the people happy 70 percent of the time, he’d consider it a victory. But with all the challenges our society has been through in the last five years, he said half-jokingly the bar for success might have slipped — 50-50, or 40-40? And his next job could be even harder.