Returns fluctuate wildly, while expenses are roughly constant. So obviously expenses are drawn conservatively. And if investment works well, you can grow the endowment too. Obviously it is up to the university to strike the right balance.

The more it grows, the less risk there is in the future. But if you start spending it below the levels of its returns, that's high risk. And the point is it's supposed to last forever.

You also need to grow it simply to account for inflation and other rising costs.