Worrying in itself is not a bad thing.
It shows you care.
When it gets to that constant and obsessive point, though, it inhibits success.
You become paralyzed by fear of making a mistake, causing you to not act.
Overthinking is a self-destructive behavior, taking a serious toll on both your mental and physical health.
You will develop anxiety, which not only causes emotional suffering, but over time will affect your heart, digestive, and nervous system, as well as many other systems in the bo.