In Endurance, the definitive account of Shackleton’s fateful trip, Alfred Lansing brilliantly narrates the voyage that has defined heroism for the last century. The crew, led by Shackleton, abandons ship and makes camp on a huge floe of pack ice. They salvage as much food and material as possible, and the expedition's dogs, sledges, and boats, are stockpiled on the floe. Although Shackleton and the crew experienced many lows, he was still able to keep them attentive and in high spirits. There are a many different reasons why we do things. Sometimes we are motivated to act because of internal desires and wishes, but at other times our behaviors are driven by a desire for external rewards. Think about what type of things motivate you to study hard and do well in school. Good grades are one type of incentive. Gaining esteem from your teachers and parents might be another. Money is also an excellent example of an external reward that motivates behavior. In many cases, these external rewards can motivate you to do things that you might otherwise avoid such as chores, work, and other tasks you might find unpleasant. Obviously, not all incentives are created equal and the rewards that you find motivating might not be enough to inspire another person to take action. Physiological, social, and cognitive factors can all play a role in what incentives you find motivating. For example, you are more likely to be motivated by food when you are actually hungry versus when you are full. Incentives can be used to get people to engage in certain behaviors, but they can also be used to get people to stop performing certain actions. Incentives only become powerful if the individual places importance on the reward. Rewards have to be obtainable in order to be motivating. For example, a student will not be motivated to earn a top grade on an exam if the assignment is so difficult that it is not realistically achievable.