---
title: "Your Estimate Isn't Off Because of Optimism or Inexperience"
date: 2026-08-15T12:15
author: Julien Reszka
description: "The real reason your estimate is too low is not wishful thinking or a lack of experience. It is what you never named out loud."
keywords: ["strategy", "decision-making", "product", "productivity"]
canonical: https://julienreszka.com/blog/your-estimate-isn-t-off-because-of-optimism-or-inexperience/
---

# Your Estimate Isn't Off Because of Optimism or Inexperience

The real reason your estimate is too low is not wishful thinking or a lack of experience. It is what you never named out loud.

Researchers asked Stanford students to estimate what share of all deaths came from different causes. When the causes were bundled into one category called unnatural causes, students estimated 32 percent. When the identical category was spelled out as accidents, homicides, or other unnatural causes, the estimate jumped to 53 percent. The real share of deaths from those causes did not change between the two questions. Only how the category was described did.

Amos Tversky and Derek Koehler built an entire theory out of that gap, now called the unpacking effect. A judgment attaches to how a category gets described, not to the event itself. Leave a category packed into one phrase and people quietly ignore the pieces they were never shown. Name the pieces out loud and the same people give it more weight, because now they are counting something they were previously skipping past.

The same pattern shows up somewhere with real deadlines attached.

- Seven professional teams estimated a 1,340 hour software project as one whole and were off by 45 percent on average
- Breaking the same project into its component parts first cut the error to 23 percent, roughly half
- A second project showed the same pattern: 55 percent error estimated whole, 31 percent estimated in parts

[Mapping the pieces of a plan before committing to a number](https://julienreszka.com/blog/napkin-sketches-beat-gantt-charts/) works for the same reason naming the causes of death worked on those Stanford students. A single global estimate lets you skip past everything you did not name. Naming the parts, even the unglamorous ones, is what forces you to actually count them.

---

**Actionable insight:** Before committing to an estimate, list the individual parts of the work by name, especially the ones you would normally lump into the rest. A number attached to a vague whole is quietly ignoring everything you did not name.

## Key figure

**45%** — Average estimation error when a professional team sized a real 1,340 hour software project as one whole, versus 23 percent after breaking it into parts first

*Source: Jorgensen, M., Top-Down and Bottom-Up Expert Estimation of Software Development Effort, Information and Software Technology, 2004*

## Myth vs reality

**Myth:** A number that comes in too low means the estimator was too optimistic, or not experienced enough.

**Reality:** Seven professional teams, not novices and no more optimistic than anyone else, misjudged a real project by 45 percent when sizing it as one whole. The same teams cut that error roughly in half just by describing the identical project in named parts instead.

*Source: Jorgensen, M., Top-Down and Bottom-Up Expert Estimation, Information and Software Technology, 2004*

## Quote

> "They indicate that probability judgments are attached not to events but to descriptions of events."
>
> — Amos Tversky and Derek Koehler, psychologists, in the paper introducing support theory

*Source: Tversky, A., Koehler, D.J., Support Theory: A Nonextensional Representation of Subjective Probability, Psychological Review, 1994*

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