Final answer:
Egoism solely focused on self-interest can lead to social disharmony and personal detriment in the long term, despite the premise of strong ethical egoism. People often engage in altruistic behavior which shows that self-interest is not the sole driver of human actions. Balancing self-interest with consideration for others is crucial for social interactions and personal well-being.
Step-by-step explanation:
The question of whether being an egoist ultimately harms oneself can be complex. Moral theories vary, but it is important to consider the impact of egoism in social settings. While strong ethical egoism holds that it is always right to aim at one's own greatest good, this viewpoint is not conducive to social harmony or establishing trust. This is because exclusive focus on self-interest can lead to transaction and conformity costs that are too high, and can harm not just others, but the egoist themselves in the long run.
On the flip side, individuals often balance self-interest with altruistic behavior. Engaging in social activities such as volunteering or helping others are examples where people do not act purely out of self-interest. Hence, while self-interest might be a starting point for economic decisions, it is not the sole driver of human behavior.
Therefore, it could be argued that being an egoist may not always be rational as it does not consider the potential long-term adverse effects to oneself and one's relationship with others. There are many instances in social life where acting beyond one's self-interest is valuable and important for overall well-being.