What makes this triangle 'dynamic' is that these three objectives continually influence one another. You cannot adjust one 'screw' without the other two sides of the triangle shifting as well, whether directly or indirectly. Here are two examples that illustrate this interdependence: Cost and performance/quality: Should you turn the cost screw and reduce the budget, this will usually affect the performance or functionality of the product. You will then have to either compromise on quality or forgo certain features.
Deadlines and costs: if a deadline absolutely must be met and you consequently need to deploy additional staff or schedule overtime, the costs of your project will rise. In short: with every decision you make in your project, you must always keep the relationships between scope, deadlines and costs in view and weigh up which compromises you can afford to make. Only then will you maintain the balance within the dynamic project triangle.