The most appropriate one-word substitution for the given group of words is egocentric.

• Egoist means "a person who is primarily interested in their own well-being or advantage."
• Egotist means "a person who is excessively conceited or self-absorbed."
• Egomaniac means "a person who has an exaggerated sense of their own importance."
• Egocentric means "having or showing an excessive or selfish regard for one's own interests, needs, or desires."

The word "egocentric" is the best fit because it conveys the idea of a person who is so focused on their own needs and desires that they are unable to consider the needs of others.