Triangle of Constraints

The Iron Triangle connects the project dimensions of scope, time and cost 

The Triangle of Constraints or Iron Triangle is a metaphor to communicate that project scope, time and cost are related.

• in the left diagram below, scope, time and cost are related because any change in one of them (eg. increase scope) require that one or two of the other dimensions be adapted
• failure to adapt causes imbalances that increase risks to the project or may be reflected in quality

• in the right diagram above, Quality and Risk are dimensions “below the water line” as they are rarely observed but should be considered: if the project is changing and nothing happens to the visible dimensions, you can expect the changes to be happening on a hidden level that involve Quality and Risk
• lower quality in software projects creates what is usually known as technical debt, to mean all work that will have to be done in the future
• when scope increases without adjustments to time and/or cost the project is said to suffer from scope creep