We all make assumptions. Wrong assumptions can have devastating impact not only on a project but also in other areas of our life.
In everyday life we make a lot of evaluations. We can evaluate the weather outlook, business or project plan, other people's behaviour, quality of our relationships, etc. Based on evaluation results we decide about our immediate or future actions. Evaluation is always based on assumptions. Some of them we realize, some of them are sort of "implicit" as we regard them as facts (e.g. that if i turn the key or push the start button, the car's engine will start). Actually, facts are just assumptions with very high probability in the current context. Assumptions can be compared to pillars of a building. If they are strong (valid assumptions), the building is solid. If they are weak (wrong assumptions), the whole building can collapse. Albert Einstein said: "Assumptions are made and most assumptions are wrong". Thus it is very important to handle assumptions efficiently.
Considering the above, we need to be aware that we're using lot of assumptions and possibly not all of them are valid. They are representing uncertainty and should be managed as potential sources of risks. Prior to important decisions/actions ask yourself: - What are the crucial assumptions that this decision is based on? - In what context and how much are these assumptions valid? - If some assumption turns out to be not valid, what impact will it have? - How can i mitigate such impact?