Dive Brief: 

• Effective Thursday, one of Yaoo CEO Marissa Mayer's first major hires, Henrique De Castro, is leaving his position as COO. 
• Mayer hired De Castro because she believed him to be responsible for Google's billion-dollar display ad business and for getting brands to advertise on YouTube. 
• Fairly quickly, De Castro's tough personality became a problem and he failed to connect with Madison Avenue, taking too long to put a sales team together, missing out on programmatic buying, and overseeing sluggish ad sales. 

Dive Insight: 

Yahoo is still in the midst of a major overhaul of its advertising business, so losing an executive could be a hardship — or it could be a huge opportunity to further turn things around. De Castro's departure is a lesson to any executive that personal relationships do matter and that a difficult personality will eventually lead to trouble.