A senior dev explained to me that waterfall is simple, everyone gets it, and it's easy to implement. There are well defined, easy, consecutive steps to be followed.
An upper manger was very keen to find ways to convince his company's leadership that waterfall fits his department really well, thus avoiding the drive to adopt agile. From his perspective, waterfall provided predictability. He new at the beginning of the year what his budget is, what projects he will be working on, and what the duration of each projects will be.
It also makes sense to design something before building it. If you don't design it before hand, how do you know what you will be building? How do you know how much it will cost? How do you decide if it's worth it? How do you compare it to other options?
In our day-to-day life, we demand predictability. Before we offer a job to a carpenter to install new kitchen cabinets, or ask a mechanic to service our car, for example, we want to know before hand how much it will cost, and how long it will take. We are really disturbed when either of these estimates are not met, although we know they are just estimates.
So what is the problem in expecting the same from software projects?
We can always give the example of an apparently simple job gone badly, as when an air conditioning engineer starts asking you when was the last time you cleaned your air vents, or changed the air filters, only to discover that you'd have to pay more and wait longer to have your air system fixed. Let's put this example aside for now.
Instead, consider the how likely is the change in your project, from inception to project end, in the following areas:
- The business needs from your application.
- The specified requirements from your application.
- Your understanding of the requirements.
- The project team's mastery of the technology.
- The people who are doing the work.
Because waterfall makes sense for certain types of projects. Software development projects are a breed of their own, with a lot of sub-varieties within.
And change is inevitable in software projects, because you'll never build the same application twice, for the same business need, with the same people, who have the same experience, using the same technology, will you?