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I have read the following about the Iron trinagle:

To add features to a product (scope), you could extend the deadline to make time for the new work (time) or add people to get it done faster (cost). You could also do both!

Well, if I extend the deadline, I will need to pay for the resources working in this extended timeline, so how can I "only" extend the deadline?

I mean, it is said you have to adjust at least one other constraint..but to me it seems it is never just one.

  • Source of the quote? – Alan Larimer Mar 26 '18 at 12:49
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The project management "iron" triangle is problematic.

  • It does not realistically represent the relationship between the three chosen aspects.
  • It does not consider quality (except, perhaps, as a result) or value provided (does it meet the needs).
  • It has been "improved" with other variations including, but not limited to,
    • Diamond which adds quality
    • PMBOK 4 double triangle which added a second triangle: risk, quality, resources
    • pick two: fast, cheap, good
    • a formula: Scope = Cost x Time

Well, if I extend the deadline, I will need to pay for the resources working in this extended timeline, so how can I "only" extend the deadline?

Exactly.

  • Thanks. The only thing I can think of would be hiring cheaper resources that would require more time (but then still the price/productivity) must be benefical for me. – John V Mar 27 '18 at 13:24
  • If you use "cheaper resources" they might be less skilled and result in even more time. They will probably also need ramp up time before becoming efficient. – Alan Larimer Mar 27 '18 at 15:11
  • It's not about the resources you hire, it's about giving it to workers you already have and getting them to 'fit it in' to their schedules when and where they have some slack. Now that places are run more efficiently, that slack is getting harder to come by, so the original quote is outdated. I see it referenced in the PMBOK 3rd Ed (p8), so it's been a while. – Gregory Morton Apr 6 '18 at 10:18
  • getting them 'to fit it in' is traditional, Taylor, whip-cracking management failing under the 100% utilization fallacy. – Alan Larimer Apr 6 '18 at 12:18
  • The people aspect of the answer and comment is related to the highlighted question. It's not about the resources you hire, it's about giving it to workers you already have makes little to no sense. – Alan Larimer Apr 6 '18 at 12:30
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Projects often spend extra to make a deadline

Alan gave a good answer pointing out the limitations of the project management "iron" triangle.

To answer your specific question, you need to consider that projects (not necessarily software projects) often plan to spend extra money to make a tight deadline. Examples of such extra spending to make a deadline are:

  1. Overtime: You may be planning to pay double time (for extra hours during week days) or triple time (weekend hours).
  2. Expedite fee: You may be planning to pay expedited fees to vendors to do rush jobs.
  3. Air freight: You may be planning to pay for air freight to get supplies from vendors earlier than if you shipped by surface freight.

If you have contract resources to whom you need to pay only for the hours actually worked, it may be possible to save money by extending the deadline. So, to answer your question:

Well, if I extend the deadline, I will need to pay for the resources working in this extended timeline, so how can I "only" extend the deadline?

As seen in the example above, if you had more time, you can avoid paying double and triple time and get increased scope of work done at same cost.

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In my opinion, this is a more accurate picture of the so called iron triangle. The three sides are related to each other but not in a finite, discreet way. The triangle is fluid, where each side affects the other two sides but, as well, other variables, including stochastic ones, impact each side or multiples sides at the same time. Imagine the lines on each side to grow and shrink in a fluid, probabilistic way.

I think the definition you posted is PM 101 and valuable to teach those just learning about this practice area, but it is far more complex than that definition, far more fluid, far less "controllable."

  • It would be great if someone could explain their negative votes. – David Espina Mar 27 '18 at 12:22
  • My thoughts FWIW . . . The modified triangle is interesting. The answer to the question regarding extending the time without increasing the cost remains unanswered or needing to be inferred. – Alan Larimer Mar 27 '18 at 15:14

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