The Missing Interface

On a complex project, every technical interface has a relationship behind it, between the two people who own it. That relationship is rarely anyone's job to manage.

Read the article How to cite it
N² + H: the same N² matrix read three times. A technical layer, an ownership layer and a health layer, with one interface highlighted through all three.
  1. Technical layerWhat must pass?
  2. Ownership layerWho is accountable?
  3. Health layerRegister statusCan the relationship carry it?Is it on track on paper?

Example project, hypothetical

Read as relationships, 10 are strong, 3 strained, 1 weak and 2 not yet formed.

Automation → Electrical

What must pass
I/O list, cable schedule and power supply requirements (many deliverables)
Who owns it
Named on both sides: the Automation lead provides, the Electrical lead receives
Relationship
Strained

Human Interface Management

Technical interface management identifies the dependencies between systems, registers them and tracks each one until it is closed. What it rarely manages is the relationship between the two people who own each interface, and that relationship affects whether the technical interface is resolved properly and in time.

Human Interface Management (HIM) is the deliberate management of that relationship. Managed together with the technical side, it forms Integrated Interface Management (IIM). The model behind it, N² + H, adds two human layers beneath each cell of the N² matrix: the owners on each side and the state of the relationship between them.

Interface Health

The bottom layer is read through five factors. Each has early warning signs that can be observed long before a deliverable is missed.

Clarity of responsibility
Does each side know who owns what, with one name accountable for it?
Communication quality
Are the two sides talking openly and in time, or sending documents back and forth and calling it coordination?
Decision speed
When a decision is needed at the boundary, does it get made, or does it sit in an inbox?
Trust
Do the two sides believe that the other will deliver, and do they tell the truth early when they cannot?
Delivery capability
Does each side have the people, the competence and the capacity to deliver what it has promised?

The article

The Missing Interface: Why Complex Projects Fail Where Nobody Is Looking

Working paper, version 1.0, October 2026. Open access on Zenodo.

Read on Zenodo doi.org/10.5281/zenodo.23426161

How to cite

Andersen, D. S. (2026). The Missing Interface: Why Complex Projects Fail Where Nobody Is Looking (Version 1.0). Zenodo. https://doi.org/10.5281/zenodo.23426161

The book

The full discipline, with its methods and tools, is set out in a forthcoming book, The Missing Interface.

Tell me when it is out

This opens an email to contact@themissinginterface.com. Your address is used only to tell you when the book is published.

The author

Danni Søndergaard Andersen is an engineer and discipline leader in energy, infrastructure and complex project delivery. ORCID: 0009-0002-0281-7797.