When we hear things like ...
Why promising nothing delivers more and planning always fails,
It's in doing the work that we discover the work that we must do,
If estimates were real the team wouldn't have to know the delivery date, they just work naturally and be on date.
You have to ask do these posters have any understanding that it's not their money? That all project work is probabilistic. That nonlinear, non-stationary, stochastic processes drive uncertainty for all work in ways that cannot be controlled by disaggregating the work (slicing), or assuming that work elements are independent from other work elements in all but the most trivial of project context.
Systems Thinking and Probability†
All systems where optimum technical performance is needed require a negative feedback loop as the basis for controlling the work in order to arrive on the planned date, with the planned capabilities, for the planned budget. If there is no need to arrive as planned or as needed, then no control system is needed, just spend until told to stop.
The negative feedback loop as a control system, is the opposite of the positive feedback loop. In chemistry a positive feedback loop is best referred to as an explosion. In project management a positive feedback loop results in a project that requires greater commitment of resources to produce the needed capabilities beyond what was anticipated. That is cost and schedule overrun and lower probability of technical success.
A project is a type of complex adaptive system that acquires information about its environment and the interactions between the project elements, identifies information of importance, and places that information within a context, model, or schema, and then acts on this information to make decisions.
The individual members of the project act as a complex adaptive system themselves and exert influence on the selection of both the schema and the adaptive forces used to make decisions. The extent to which learning produces adaptive or maladaptive behavior determines the survival of failure of the project and the organization producing the value from the project.
Managing in the Presence of Uncertainty
Uncertainty creates risk. Reducible risk and irreducible risk. This risk by its nature is probabilistic. Complex systems tend to organize themselves in a normal distribution of outcomes ONLY if each individual element of the system is Independent and Identically distributed. If this is not the case, long tailed distributions result and are the source of Black Swans. And these Black Swans are unanticipated cost and schedule performance problems and technical failures we are familiar with in the literature. The project explodes.
So We Arrive at the End
To manage in the presence of an uncertain future for cost, delivery date, and delivered capabilities to produce the value in exchange for the cost, we need some mechanism to inform our decision making process based on these random variables. The random variables that create risk. Risk that must be reduced to increase the probability of success. The reducible risk and the irreducible risk.
This mechanism is the ability to estimate to impact of any decision while making the trade off between decision alternatives - this is the basis of Microeconomics - the tradeoff of a decision based on the opportunity cost of the collection of decision alternatives.
Anyone conjecturing that decisions can be made in the presence of uncertainty without making estimated impacts of those decisions has willfully ignored the foundational principles of Microeconomics.
The only possible way to make decisions in the absence of estimating the impact of a decision is when the decision has a trivial value at risk. Many decisions are just that. If I decide wrong the outcome has little or no impact on cost, schedule, or needed technical performance. In this case Not Estimating is a viable option. For all other conditions, Not Estimates results in a Black Swan explosion of the customers budget, time line, and expected beneficial outcomes based on the produced value.
† Technical Performance Measurement, Earned Value, and Risk Management: An Integrated Diagnostic Tool for Program Management, Commander N. D. Pisano, SC, USN, Program Executive Officer Air NSW, Assault and Special Missions Programs (PEO(A)). Nick is a colleague. This paper is from 1991 defining how to plan and assess performance for complex, emergent systems.