What are the common mistakes people make when planning to achieve their goals and what psychological processes promote them?

What will be an ideal response?

a . People tend to be overly optimistic when planning how to reach their goals. This optimistic bias, called the planning fallacy, tends to lead people to underestimate how long it might take to achieve a goal, how much it may cost to achieve the goal, and so forth.
b. People's positive illusions about themselves tend to promote the planning fallacy. While people can predict how long it might take someone else to achieve a goal, they underestimate how long it might take for themselves to accomplish a task set as a goal.
c. Goals that are in the distant future tend to be most susceptible to the planning fallacy. As goals loom nearer in time, they are less likely to be subject to the optimism that taints plans for distal goals. Distal goals are not as subject to practical constraints that become more obvious as the goal becomes more proximal.