I mean I was taught the waterfall model in school. Our teacher praised as the most used model in the industry.

However I was taught that at any stage of the model you can go back one and re-evaluate the problems and solutions.

Now today I don’t know anyone who really uses this model in it’s pure or wrong form. Reason beeing that the client always wants to add a feature mid implementation. And then you can throw all your planning and design out of the window and start again.

Saying no to the client is rarely an option since you want to be paid for your work.