As the overlapping costs required to reduce the project makespan by one unit time increase, it may outweigh the opportunity cost. Figure 3 shows that project gain decreases when activities are overlapped beyond a certain point. This explains why the optimal makespan obtained with the project gain maximization problem in the previous section differs from the minimal makespan. Depending on the resource availability and how much the project managers and planners are willing to pay to complete the project earlier, the time-cost trade-off analysis presented in this section should help them to choose an appropriate overlapping strategy.