The term triple constraint is sometimes used to refer to three common constraints: cost, scope, and time. In many cases, these constraints can be "traded-off". For instance, if the project must be completed sooner, you can shorten the schedule by increasing the cost -- hiring more staff or paying extra for materials or expedited shipping. Or, you could reduce the time by decreasing the scope -- choosing to remove non-essential features. Alternatively, if additional features must be added to the scope, it will require more money and/or time. Similarly the cost can be reduced by limiting the scope or adding time to the schedule. These trade-offs are not always clear-cut. For instance, adding staff will not reduce the time, if the staff takes too much time to hire, train, or bring up-to-date with project knowledge.