• It satisfies our preference for simplicity. In science, we favour theories that explain several phenomena by showing them to all be controlled by the same force. Newton's theory of gravity gives one principle to explain a falling apple.
• It offers a seemingly cynical view of human nature. It appeals to our concern not to be naive.

To the critics, the theory is too simple. Being hard-headed is not a virtue if it means ignoring contrary evidence. Most of us have a natural concern for others, perhaps because we are social beings by nature.

The most obvious objection to psychological egoism is that there are numerous clear examples of people putting others' interests before their own.

Although psychological egoists think they can explain seemingly virtuous actions, their theory rests on a false account of hu...