Waterfall advocates that we do a significant amount of design upfront. But it’s not possible to do it all up upfront. That never happens in any traditional project.
Scrum advocated that we should not over design as the customers/user doesn’t know what they want. Therefore spending time investigating would be wasted. Let’s build it and as we develop, check with the customer to see if it’s what they want.
Importantly, Scrum is not a series of mini waterfalls where we design for a few days and then build then test the next few days. We should do the design, develop and test at the same time. Removing the upfront design effort and merging it with the build. Chances are, it will take the same amount of energy to design and build, but it will be what the customer wants – better quality. And we have maximised the amount of work not-done by not delivering what the customer did not need.