NPV vs. IRR someone, discount, budgeting, sometimes, following

stronger

Could someone explain the following:

It is sometimes siad that NPV implicitly assumes that project cash flows can be reinvested at the discount rate used to calculate NPV.

If we were to rank projects by their IRRs, we would be implictly assuming that project cash flows could be reinvested at the project's IRR.

This is from Kaplan Capital budgeting page 25.