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The aim of this technique is to make underlying assumptions more visible.
- Identify a particular choice you have made, and ask yourself why you feel it is the best choice – i.e. what assumptions guide this choice.
- List the assumptions, and beside each write a counter-assumption - not necessarily its negation, but the opposite to the issue it represents.
- Work down the list and delete ineffective assumption/counter-assumption pairs i.e. where it would make little difference to your choice whether the assumption or the counter-assumption were actually the case.
- Assess each of the remaining assumptions in terms of high or low potential impact (how critical is its truth to justifying your pattern of behaviour?) and high or low plausibility (how confident are you that it is, in fact, true?).
- Plot the assumptions on a 2x2 matrix (high/low impact on one axis, high/low plausibility on the other).
High impact/high plausibility assumptions are clearly the most crucial, but high impact/low plausibility assumptions need to be taken seriously, in case they turn out to be true, so check them out if you can.
The assumptions in the ‘high impact’ cells are those that the user sees as largely justifying their actions. Are they over-estimating them? What could change these assumptions? What benefits would there be and for whom?
The assumptions in the ‘low impact’ cells are seen as less critical, but it might be worth checking this out – are they being under-estimated?