Imagine two project teams, Team A and Team B. They take on exactly the same work. Team A does a poor and hasty job of planning, and the project manager commits to complete the work in 12 months, at a cost of US$1 million. Team B does a more careful job of planning, and the project manager commits to complete exactly the same work in 14 months, at a cost of US$1.2 million.
Teams A and B deliver precisely the same result, at the same cost, in the same amount of time. Total project duration: 13 months. Total project cost: US$1.1 million.
But consider how they're evaluated:
"Project Team A Exceeds Budget by $100,000, Delivered Late. Project Manager is Fired."
"Project Team B Delivered Early and Under Budget. Celebration in Honor of Project Manager."
The essential difference between a well-managed project and a poorly managed one is, in my estimation, entirely in the planning. Planning is about the creation of expectations. In this case, expectations were created and then either fulfilled or not, with all other factors being equal.
What do you think: Does successful project planning create a successful project management career?


My two cents: both evaluations are wrong.
First one delivered the project one month late at 100K over budget while the second one delivered the project one month earlier at 100K under budget.
Assuming some well defined value of accepted tolerances in terms of budget and time both PMs delivered "same performance" but, with plus or minus sign in front of the budget / time indicator at the end.
Celebration in honor of the second PM would create a precedent in that company to over-estimate all future projects, which may lead to increase the cash - flow and debt without reasons.
Best would be to define an acceptance criteria , i.e +/-5% accepted budget deviation at the end or +/-10% accepted deviation in time. That means in one word, best definition of the project scope - including the acceptance criteria. When the project scope is defined? At the beginning of the project, surely, and further more, it should be agreed by project sponsor.
You are preaching the obvious to all with project management practical experience. The old motto of "plan the work and work the plan" remains a valid and wise guiding light.