This question focuses on the challenges individuals face when managing their goals. The correct answer is 'D' because an inability to maintain focus on tasks can lead to a struggle with managing goals. Option 'A' is incorrect because overestimating capabilities can lead to setting unrealistic goals but does not directly relate to the struggle in managing them. Option 'B' is incorrect because underestimating the importance of goals would not necessarily cause management issues. Option 'C' is incorrect because difficulty in setting clear objectives is a separate issue from managing goals that have already been set.