Systems development life cycle (SDLC) when performed well can provide a more efficient means of delivering IT systems. I would have to say that the analysis phase would prove most critical. This is where the idea of what the product is supposed to do begins to comes to life. It is at this stage that input is gathered from the end user, as well as the technical experts, and an evaluation of capabilities is conducted. Many important questions are answered and there is actually a tangible model of what, and how the IT system will function. This is where the decision of the prototype is made, and can make or break the funding needed to continue forward with the product or not. Inexperience in this area can prevent an otherwise great idea from reaching full development.
I believe all SLDC phases are essential during the process as they need to be carried out for the process to be successful. I agreed with Prof. Eugster; the analysis is the most important part of the first process during the SDLC phase. Analysis phase has to do with requirement gathering. The analysis phase is one of the primary focus of project management and stakeholders. This phase is where a steering committee is formed to determining who will be using the system, how will the system be used? What data that need to be input and output in the system, et cetera. when is analysis phase process is completed a requirement specification document is created to guide the remaining phases.
What drives the implementation? The two earlier phases; planning and analysis.
If there are errors or missing info from these two phases, the implementation will be wrong.