The number of people who would have to be lost before a project stalls, which is usually one.
Ask which single absence would halt the project. The honest answer is usually one person, and usually not the one on the org chart.
In practice
- A finance team's month-end close depends entirely on one analyst's undocumented workbook, and everyone knows her holiday dates.
- A charity's grant applications are written by one trustee, and the funding cliff arrives with her retirement.
- Further reading
- Wikipedia
- Subject
- Organizations & Bureaucracy
- Essay
- The folklore of office life