What is the difference between two photos below?
Yes, you are right – without the mist we can see the building more clearly. Something similar is happening with our projects: early in the initiation stage, there is a lot of uncertainty. It is really hard to estimate time and cost requirements, especially when the scope of work is not clearly defined.
However, it is still important to come up with an estimate, even if it is very high-level. Ideally, we have to define a way to manage the scope, schedule, requirements, financials, quality, resources, change, risks, stakeholders, communications, etc. Later in the project we can progressively elaborate on the plan to make it more accurate.
As far as an initial estimate for a timelines goes, even creating a list of activities and understanding dependencies can dramatically reduce the fog.
Try engaging your team members: ask them how long they think certain work packages might take to complete. Organise a workshop to discuss and capture the dependencies and risks. Make sure you have buy-in from your team and everyone is aware of the critical path
Yes, things can and will change, but having a plan helps you to become more aware of the potential impact of this change on budget, scope or quality. Ultimately, a good plan can help project managers put things into perspective and monitor and control projects more effectively.