Philip Marris presents the two dimensions of constraints in projects: the portfolio constraint and the constraint that is intrinsic to each project.

The first one will be a resource or a department in the enterprise. Because of the availability of the constraint it will not be possible to initiate more projects in your company. For instance, in new product development it could be the prototyping department.

The second one is the project constraint, it is its Critical Chain. This constraint will define the project duration.

To unblottleneck you projects you can act on those two parameters: you can try to reduce your Critical Chain for all your projects and can also try to increase the capacity of your bottleneck resource or department.