Planning after the action

This idea is loosely borrowed from the extreme programming paradigm of software development.

Essentially the idea of planning in Extreme programming is - Just plan the next step, Then execute, Learn and then Refine the plan. This saves time and cost.

I have a brief suggestion:

No matter what kind of project planning you do, whether extreme or “normal big bang” planning, After you finished your work on any stage.. Go back to your planning and update the plan with what you actually spent in terms of resources and time. The next time you have a project that includes these elements, you can copy paste the relevant sections of the “executed plan”, and have a more realistic idea of how things will unfold..

A side benefit - you know who you want on your team the next time around as well if you do this.