The word "obsessive" can best be characterized as:

The term "obsessive" is best characterized by the notion of being excessively focused on something. This word often implies an intense preoccupation that can dominate an individual's thoughts and actions, leading to a lack of balance in their life. The intensity associated with being obsessive can manifest in various contexts, such as relationships, hobbies, or compulsive behaviors, where the person finds it challenging to divert their attention away from the object of their fixation.

This focus is often problematic, as it can interfere with daily functioning and relationships, highlighting why the characteristic of being excessively focused aligns so well with the definition of "obsessive." The other options do not capture the essence of the term: balance and stability suggest moderation rather than fixation; living in isolation refers to a physical or emotional distance from others rather than focus; and being indifferent to feelings implies a lack of emotional response, which does not inherently relate to obsession.