Here are some synonyms for "overzealous":
* Fanatical
* Overenthusiastic
* Overeager
* Over-the-top
* Exuberant (but often used in a positive way)
Examples:
* "The overzealous salesman pressured me into buying a product I didn't need."
* "Her overzealous cleaning led to the destruction of several family heirlooms."
* "The overzealous fans caused a riot after their team lost the championship."
Being overzealous can be problematic because it can lead to:
* Mistakes due to a lack of careful consideration
* Offending others by being too pushy or aggressive
* Negative outcomes by going too far in pursuit of a goal
It's important to be enthusiastic and passionate, but it's also important to be mindful and maintain a balance.