The number one reason is overlooking context.

Context is a critical component of successful leadership. A brilliant leader in one situation does not necessarily perform well in another. Academic studies have shown this, and our experience bears it out. The CEO of a large European services business we know had an outstanding record when markets were growing quickly, but he failed to provide clear direction or to impose financial discipline on the group’s business units during the most recent economic downturn. Instead, he continued to encourage innovation and new thinking—hallmarks of the culture that had previously brought success—until he was finally replaced for underperformance.

Context matters.