An agent – or a sector of the economy – that contracts a net debt has implicitly chosen to bring forward resources to the present, thus reducing them in the future, in order to pay off that debt (provided, of course, that it does not intend to renege on its debt obligations!).
Financial stability can be defined as a situation in which the intertemporal allocation of resources is felt to be “in equilibrium” or “sustainable”, which means that it is at the same time in line with the desires of individual agents and with the need to keep up with the debt obligations that have been subscribed.