As in real life the network included a mixture of large and small banks. The researchers found that large banks were particularly important during a crisis. If one collapsed, it could have a surprisingly big impact on the health of other firms. Allowing the large banks to hold a more diverse range of assets didn't necessarily help protect the network either. More diversification meant a larger overall number of exposures. So if a big bank started selling off all these different assets to avoid bankruptcy, any other banks that held these assets would be affected too. Diversification might help stabilise an individual bank, but it can destabilise the network as a whole.