Business thinker

Taiichi Ohno's 5 whys and seven wastes

Updated 4 November 2026

Not affiliated with or endorsed by Taiichi Ohno or their companies.

Taiichi Ohno helped establish the Toyota Production System; Toyota credits him with creating the basic framework of Just-in-Time, with strong backing from Eiji Toyoda. Two ideas he set out are used far beyond car plants: asking why repeatedly until you reach the root cause of a problem, and sorting what you see into seven wastes. This page explains both from Toyota's and the Lean Enterprise Institute's material, and shows how to apply them to office and service work.

The 5 whys: from symptom to root cause

The Lean Enterprise Institute (LEI) defines the 5 whys as asking why repeatedly whenever a problem is encountered, to get beyond the obvious symptoms to the root cause. Its example is the one Ohno gives in his book (cited by LEI as Ohno 1988, the English edition): a machine that stopped working.

The machine stopped because an overload blew the fuse. The overload happened because a bearing wasn't lubricated enough, because the lubrication pump wasn't pumping enough, because the pump's shaft was worn and rattling, because there was no strainer and metal scraps got in. Without asking why, the fuse or the pump would be replaced and the failure would come back.

LEI adds that the specific number five is not the point: keep asking until the root cause is reached and eliminated.

The same works on a desk. If 12 of 140 orders shipped a day late last week, the chain might run: labels weren't printed in time, the printer jammed, it was a year overdue for service, nobody owns the printer. The last answer is a gap in the process, not a person who forgot.

The seven wastes: name what you see

LEI calls the seven wastes Ohno's categorisation of the major wastes typically found in mass production:

• Overproduction: producing ahead of what the next process or customer needs. The worst, because it contributes to the other six.
• Waiting: people standing idle while machines cycle, equipment fails or parts don't arrive.
• Conveyance: moving parts and products unnecessarily.
• Processing: unnecessary or incorrect processing, often from poor tool or product design.
• Inventory: more than the minimum stock a pull system needs.
• Motion: straining or unnecessary movement, such as looking for parts, tools or documents.
• Correction: inspection, rework and scrap.

LEI also says to see work before waste. Work splits into value-creating work (welding, drilling, painting), incidental work that is needed now but adds nothing the customer values (reaching for a tool, clamping a fixture), and waste that creates no value and can be removed.

In an office, waiting for an approval is waiting, re-keying between tools is conveyance, pricing options nobody asked for is overproduction, searching and window-switching is motion, and a quote sent back for fixes is correction. That mapping is our adaptation, not the sources'.

Where they sit in the Toyota Production System

Toyota describes its production system as based on the complete elimination of waste in pursuit of the most efficient methods. Its stated objective, on the premise of making work easier for workers, is to eliminate waste thoroughly and shorten lead times so customers get vehicles quickly, at low cost and with high quality. Both tools serve that aim: find the waste in a process, remove its cause, and check that lead time went down.

How to apply it to your own work

1. State the problem as a measured gap from the standard ("12 of 140 orders shipped late, against same-day dispatch").
2. Ask why, and write the fact behind each answer; don't move on from an answer that has none.
3. Read the chain backwards with "therefore" to check that it holds.
4. When you reach a gap in the process rather than a person, set one countermeasure for the root cause and, if needed, one for containment now.
5. On another day, write out one process step by step with work time and wait time.
6. Label each step value-creating, incidental or waste, name the waste type, and look for overproduction first.

What the sources say, and what they don't

The stopped-machine example and the definitions of the seven wastes come from LEI's lexicon, which cites Ohno's book; the aim of the system and Ohno's role come from Toyota's own description. The office translations of the wastes are our adaptation. Nothing on this page quotes Ohno's book directly.