Anson Chan's explanation about why she decided to quit 14 months early is not entirely convincing. On the sensitive question of whether she will run for the post of Chief Executive, she has by no means categorically ruled out the possibility.
Mrs Chan's assertion that her work is done because the worst of the economic crisis is over is not the whole truth. Indeed, the Chief Executive and top officials admit many people have yet to benefit from the rebound. Worse still, the increasing disparity in income between the rich and poor is poised to become a serious social problem for the future administration.
While it is true the civil service revamp is mostly complete, the much more politically sensitive issue of a new system of political accountability remains on the drawing board. The new system's impact on the values, culture and continuity of senior civil servants could be big.
Mrs Chan may have found she no longer had a role in shaping the long-term agenda of the administration. By early next year, there probably will be only one item on the political agenda - the election of the second chief executive. No major policy initiatives are likely to be introduced while the leadership is technically in transition.
Mrs Chan's calls for her successor to come from within the civil service suggest continuity at the top figured high in her decision. Known as a strong defender of the system, the last thing Mrs Chan wants is to have the civil service headed by a political appointee.
Whether a calculated move or an inevitable scenario, her unexpected departure will effectively limit Mr Tung's choice of successor. For the sake of continuity and morale-boosting, the post will go to Donald Tsang.