Monomania (noun)

1. A condition characterized by excessive focus or obsession on a single thing or idea.
2. An excessive or irrational preoccupation with a single subject or idea.

Origin:

From the word "mono-" meaning one and "mania" meaning madness or obsession.

Examples:

1. His monomania for collecting stamps consumed all his spare time and money.
2. She was diagnosed with monomania for cleanliness and spent hours cleaning her house every day.
3. His monomania for work was causing him to neglect his family.
4. The stock market crash was blamed on the monomania of investors for technology stocks.
5. His monomania for playing video games led to him losing his job and his relationships.