Pay attention to the language we use here. It may seem to be a simple wording change but it will have significant implications.
Every time you provide a delivery commitment, ask yourself, “What’s the chance of meeting that goal”? And if the approach you use to make delivery predictions doesn’t enable you to quantify that probability, it’s worth considering an alternative.
Remember, the main purpose of estimating is to manage risks effectively. There’s always risk involved and the most effective approach to managing realistic expectations is to quantify that risk by assessing the probability of achieving your goals.
The vertical percentile lines on the distribution communicate the risk you’re managing! The probabilities that the simulation produces (50%, 70%, 85%, 95%, 98%) quantify that risk in terms of percentages.
The question is no longer “When you will deliver?”, the question is now “How much risk are you willing to take?”
If you plan with less confidence – let’s say you commit to delivering before the 27th of March on the 50th percentile (which is, by the way, the same confidence level that comes with flipping a coin!) – you really ought to ask yourself whether you want to manage that level of risk.
We want to mitigate the risk of failure as much as we can. 50% certainty is very low. Ideally, you should be working with 70%, 85%, or even 95% certainty when you’re making your delivery commitments.
Here is how I want you to think about it:
If you commit to the delivery date on the 50th percentile, you will be wrong 1 out of every 2 times. If you commit to the date on the 85th percentile, you will be wrong 1 out of every 7 times. If you go for the 95th percentile, the risk of failure drops down to 1 out of 20 times.
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