Here's why:
* Chimera: In Greek mythology, a chimera was a monstrous creature with the head of a lion, the body of a goat, and the tail of a serpent. It was a product of fantasy, something that couldn't exist in reality.
* Chasing: This implies a determined effort to obtain something.
Therefore, "chasing a chimera" suggests pursuing a goal that is inherently unrealistic, like:
* Trying to find a pot of gold at the end of a rainbow.
* Searching for a cure for a disease that has no known treatment.
* Hoping for a relationship with someone who will never reciprocate your feelings.
In essence, chasing a chimera is a waste of time and energy, because the goal is fundamentally impossible to achieve.