[steveBK123]

The assumptions in that math are wrong anyway. Once you depend on 10 people, the chance that they each achieve "95% successful execution" is 0.

This is only partially down to the impossibility of having every staff member on a project be A++ players.

There is coordination RISK not just coordination overhead. Think planning a 2 week trip with your spouse with multiple planes/trains/hotels, museum/exhibit ticket bookings, meal reservations, etc. Inevitably something gets misunderstood/miscommunicated between the two of you and therefore mis-implemented.

Now add more communication nodes to the graph and watch the error rate explode.

[nostrademons]

That's what the math is reflecting. Project succeeds if all of 10 people does their job well. Each person has a 95% chance of succeeding. 0.95^10 ~= 60%, and so the chance that all 10 people do their job successfully is ~60%.

Those jobs also include things like management and product design, and so the coordination risk is reflected in the 5% chance that the manager drops the ball on communication. (As a manager, I suspect that chance is significantly more than 5% and that's why overall success rates are even lower.)

[steveBK123]

That's what I mean "only 5%" encapsulating all failure modes (comms/implementation/coordination/etc) is very low.

And that under-estimation compounds to make the top level 60% much higher than it should be.

A 7.5% rate takes top-level success odds below 50% - 46%. A not unrealistic 10% takes the top level down to 35%.

Etc.

[econ]

For extra fun we are doing more than one project in a row.