The article talks about how private investors can help pay for big projects like high-speed rail. To make these projects work with private money, it's important to understand the project's economics, get the right laws and contracts in place, and pick the best way to finance it. They need to look at best and worst-case scenarios to make sure the project makes money. Mixing public and private money can be a good idea and can help lower risks. When done right, private investment can make profitable projects even better, but public authorities play a key role in controlling infrastructure projects.