It's important for us to be humble. What I mean by that is that investment income is only one of the components that drive sustainability, which is measured on a 75-year horizon. Historically, not to get too technical, if I think of the different accounts, there's the base CPP and, after recent reforms about four or five years ago, there's the additional CPP. They're structured differently.
The base CPP is largely dependent on economic and demographic factors, such as immigration rates, fertility rates, mortality and, obviously, net income. With the additional CPP, because it's fully funded, a greater part of that account is dependent on net income. What that means is that we're working really hard, under John's strategy and leadership. It's very important for us to lean in on those important words created by parliamentarians around maximizing returns. The more returns we produce, the more we create additional buffers against those other factors outside of our control.
It would be difficult for us to make a promise to Canadians and say the fund will continue to be sustainable forever. There are a number of factors we don't control.