Two stories about a link
A connection can spread resources and absorb a disturbance. It can also transmit a dependency that carries failure onward. Whether a new connection helps depends on what the link means, how strong it is and how the system responds to shocks.
A formal example
Acemoglu, Ozdaglar and Tahbaz-Salehi study networks of financial obligations. In their model, connectivity can make a network better able to absorb sufficiently small shocks, while the same connections can transmit sufficiently large shocks more widely. Shock size and the structure of liabilities matter together.
TRY THE MECHANISM / NETWORK CASCADE
How far can one loss travel?
Nine counterparties. The same obligations. Change the loss at A and watch the repayment shortfall spread.
Run the model to trace unpaid obligations.
Teaching model · assumptions
Nine identical counterparties each have 108 units of external assets, owe 100 to senior outside creditors, and owe 80 split equally among the other eight. With full interbank payments, the initial equity buffer is 8. A loses 0–108 external units. Every clearing iteration pays senior creditors first, then distributes available assets proportionally to interbank creditors. Unpaid obligations become the creditors’ losses at the next iteration. Edges carry repayment shortfalls, not physical cash moving along animated paths.
This original toy illustrates shock-size dependence using a fixed, fully connected network. It does not reproduce Acemoglu and colleagues’ full model or establish their comparison across network structures. No fire sales, rescue, common shocks or liquidity runs are included. The iteration is a clearing calculation, not a calibrated time interval.
The boundary of the result
This is a mathematical result under specified assumptions about counterparties and obligations. Other channels, such as common-asset fire sales and funding withdrawals, are not the central mechanism of the inspected model. The paper is not a forecast for a particular financial institution.
A useful design question
Before adding a connection, state what it carries during ordinary operation and what it carries during failure. Ask which dependencies are shared, whether a disturbance can be contained, and what isolation would cost. “More connected” is not a sufficient design objective.