In modern society, multitasking is necessary for a worker to accomplish a final goal by their deadline, which could be pursued for either a single goal or multiple goals. Moreover, a worker who has the authority to prioritize their tasks can make plans about the process of behavioral strategies to perform each task by making a to-do list. This strategy is a way of unpacking that which seems to affect the expectancy of goal attainment and heighten the value and importance of the goal. Otherwise, a worker could write a to-do list without specific action plans. These effects of unpacking and packing can be used as management strategies for multitasking engagement and could impact a worker’s cognition differently depending on the goal relations, including if there is a single goal or multiple goals. On the one hand, in pursuit of a single goal, unpacking can facilitate a worker’s judgment of the importance of the task. On the other hand, in pursuit of multiple goals, a worker’s judgment of one task’s importance can conflict with another task due to contradictory unpacking guidelines. Additionally, self-regulation as an intrinsic motivation empowers conscious intentions to neglect the cognitive effects of the to-do list. Therefore, those with low self-regulation tend to be encouraged by the effect of unpacking, but those with high self-regulation have the effects of unpacking inhibited. This theoretical model was constructed to identify the cognitive mechanism and the role of self-regulation on boundary conditions in regard to the different effects on unpacking. This study was confirmed via the two-way experiment (single- and multiple-goal x packing and unpacking) to explore the effects of the cognitive mechanism on task importance. The following test was performed via the three-way experiment, using an additional variable, the levels of self-regulation (low self-regulation and high self-regulation), to verify whether they inhibit cognitive effects. This study suggests that the judgment of task importance is different in accordance with goal relations, packing and unpacking, and self-regulations for sustainable management strategies of multitasking.