I think the mission of an agile coach is to keep a project on the road to success. He monitors the effectiveness of the team and makes adjustments as necessary.

My father compares parenting to bumper bowling; a parent's job is to keep the ball out of the gutter. But, if their child is not approaching the edge, the parent should let the child find his own way.

Similarly, a good coach provides guidance but allows (and hopefully encourages) a team to find their own identity. It's critical for a team to take ownership of its own process if they are to maintain and adopt it. In my experience, a team will not maintain or effectively utilize an agile process, over the long term, if the coach is the only champion of the process.

Returning to the parenting analogy, the early stages of a child's development are where the parent's role is the clearest; the world is fairly black and white. But as the child develops into a teenager and young adult, the situations, decisions and consequences are more complicated.

The same is true for an agile coach. In the early stages of the coach's involvement, the team is the most willing, as they will ever be to take advice on faith. The coach can demonstrate techniques, discuss experiences and respond to questions; but the expectations of the coach are largely about process. At this time, the coach is relying on her own abilities to communicate the effectiveness and motivation of agile processes; this is the most amount of control the coach will have.

But as with the developing child, things get complicated. As the project ensues, the expectations quickly shift from process to results. Where the customer was happy to see any piece of working software in the beginning, she now has expectations of high productivity. The coach is now relying on the aptitude of the team; the coach has less direct control and must mentor the team such that they produce effectively.

As the expectations of the team increase, credibility and trust are necessary for effective coaching. Any latitude the coach will have with the team, be it management or developers, will be based on the experience of the team with the coach. It is a form of currency; successes are credits and problems are debits.

Each adjustment the coach makes is also a debit. The more direct (i.e. dictatorial or authoritative) the action, the larger the debit; subtle actions cost less. The coach has to be careful not to bankrupt herself; the skillful and wise coach judiciously spends in order to maintain reserves. A team is far more likely to trust a coach when she directly and obviously intervenes if they don't feel she is constantly crying wolf.

The master coach facilitates success by influence and suggestion. A coach shouldn't issue mandates. A good coach is a catalyst and his coaching, at times, is imperceptible. But a team usually knows when they have a good coach.