Completing a project on time and on budget is the dream of any project manager. Nevertheless, most projects are delayed, and the estimate exceeds the planned. This is due to the variability of processes: an unexpected shortage of people, overloading of workshops, equipment failures, problems with contractors and quality. An attempt to tighten planning does not lead to anything: life still brings surprises that are not in the plan. The key to effective project management is to take into account variability using the critical chain method, which is developed on the basis of Goldratt's constraint theory and Deming's statistical approach.