For example, a project can be completed faster by increasing budget or cutting scope. Similarly, increasing scope may require equivalent increases in budget and schedule. Cutting budget without adjusting schedule or scope will lead to lower quality.
In practice, however, trading between constraints is not always possible. For example, throwing money (and people) at a fully staffed project can slow it down. Moreover, in poorly run projects it is often impossible to improve budget, schedule or scope without adversely affecting quality.
The Project Management Triangle is used to analyze projects. It is often misused to define success as delivering the required scope, at a reasonable quality, within the established budget and schedule. The Project Management Triangle is clearly insufficient as a model of project success because it omits crucial dimensions of success including impact on stakeholders, learning and user satisfaction.
The time constraint refers to the amount of time available to complete a project. The cost constraint refers to the budgeted amount available for the project. The scope constraint refers to what must be done to produce the project's end result. These three constraints are often competing constraints: increased scope typically means increased time and increased cost, a tight time constraint could mean increased costs and reduced scope, and a tight budget could mean increased time and reduced scope.