This article considers the fall of New Zealand's first coalition government under the Mixed Member Proportional (MMP) electoral system, through the prism of a 'unified' model of Cabinet durability. This model incorporates both the 'structural attributes' of the government at the time of its formation, as well as the stochastic 'critical events' that occur over its lifetime. However, the conventional attributes of the National-New Zealand First coalition were considered favourable, and the critical event that precipitated its demise did not by itself appear to be a sufficient condition for termination. It is argued that the hitherto unspecified structural attribute of intra-party stability was a significant factor for this particular coalition, and that this case also demonstrates the cumulative impact of non-terminal events in undermining the incentives for continued cooperation between coalition partners.