MicrosoftВ® Office Project 2007 Step by Step (Step By Step (Microsoft))

When addressing variance in a project plan, it is useful to evaluate your plan (and variance) in terms of time, cost, and scope: the three sides of the project triangle.

When addressing schedule problems, focus your remedies on tasks on the critical path; these drive the finish date of the project.

When addressing cost or scope problems, focus on expensive resources and especially on their longer assignments.