Symbian for Software Leaders: Principles of Successful Smartphone Development Projects

Chapter 13. Managing uncertainty

The 80–20 rule for planning

One of the most useful rules in successful projects – as in life generally – is the 80–20 rule: 80% of the possible value of an activity can be obtained by careful application of 20% of the possible effort. Conversely, 80% of the problems can arise from just 20% of the causes. For example,

• 20% of customers can account for about 80% of sales revenue

• 20% of the add-on applications can account for 80% of the sales of add-on applications

• 20% of the software engineers can cause 80% of the defects

• 80% of what you achieve in your job can come from 20% of the time spent

• 80% of the time on a smartphone is spent executing around 20% of its operating code

• 80% of the heartache in a smartphone project will be caused by 20% of the project tasks.

Of course, the numbers 80 and 20 aren't exact. In a given field of enterprise, it might be a 75–30 rule, or a 60–15 rule, or a 95–25 rule, instead of 80–20. But the point is that it's not 50–50. In other words, not all effort is equal. It's a very ineffective approach to try to refine and improve all aspects of a project plan at once. Instead, you have to identify the parts of the project that will have the biggest impact on the overall schedule. These are the parts that you need to plan in most detail.

Even before that decision, you have to identify the parts of the new functionality of the product that are the most important. These are the features that absolutely must be in the product – the "mandatory" ...