Agile and the Overachiever
With an overachiever, a common theme emerges of the hero pushing aside the team. The values of the agile manifesto—that people are important—become hollow words, Products are no longer built around motivated individuals (emphasis on the plural), but are built around an individual. As the Agile Manifesto states: “Build projects around motivated individuals. Give them the environment and the support they need, and trust them to get the job done.”  Note that this refers to “motivated individuals” working collaboratively, not to individual contributors working alone. The effect of an overachiever can mitigate many of the great principles of the Agile Manifesto. For example, the manifesto states: “The best architectures, requirements, and designs emerge from self-organizing teams.” . Too much emphasis on the individual is the opposite of what Larman and Adkins so aptly described in Agile and Iterative Development: a Manager's Guide and Coaching Agile Teams.
Agile development emphasizes decentralized and lateral control structures and reciprocal power relations and encourages employee creativity and initiative by putting the context of the work squarely on the shoulders of the team. Team members must be comfortable enough to make mistakes; otherwise, the team cannot develop and use its abilities. Leadership must promote acceptance of ambiguity, facilitate collaborative teamwork, and promote exploration . Leaders—through formal training, individual discussions, and example—must coach the team on effective group dynamics, build the team’s confidence, and help team members embrace ambiguity .
In an agile environment, the team should be the center of work and productivity. Yet, each sprint provides an opportunity for the hero to pull out the stops and meet the sprint goal. This can become a positive feedback loop for the overachiever, who is gratified by his contribution. This behavior artificially inflates velocity since the team completes more work than is possible under a sustainable pace. Eventually this rush to completion at all costs leads to another iteration of overly optimistic commitments.
An overachiever may hoard tasks or even whole stories, ensuring that he is the center of the team’s effort. Even pair programming  can provide an opportunity for an overachiever to show off as he reduces his partner to a passive observer.