The Agile Manifesto is a leadership mindset, consisting of values and principles. It is neither a methodology, nor a process framework. The first value pair is “Individuals and interactions over processes and tools”. Please note: there is over, not instead of. The Manifesto is an appeal for change, a response to the failure of the dominant software development project management paradigms, and that, of course, includes also the so-called Waterfall process.
Scrum is an Inspect&Adapt-Framework for successful product development that establishes short feedback loops to cope with complexity and risk. Scrum deals with the question: “Are we doing the right thing?” For this purpose, the customer should be deeply involved. And yes, Scrum is part of the Agile movement. But it’s not the only one.
These two things should never be mixed.
Of course, there are many really bad implementations of Scrum out there. Some of them don’t deserve to be called Scrum at all. Sometimes the management just heard about this crazy new thing and decided: We need that too! But they didn’t really understood the purpose to do software development that way, in the era of ever-increasing complexity.
Sir Winston Royce can be called the inventor of waterfall. He described the waterfall process as an easy way to develop software, which works only for the most easiest and simplest projects. Think about it.