"Good is the enemy of Great." - Jim Collins
There's nothing inherently wrong with "good" except when it's used for measurement. For example...
Lack of honest feedback. When you ask for an evaluation and the only response you get is "it was good," then someone's lying. "Good" is a vague, non-descriptive answer. If you really want to be helpful, be truthful and specific. Don't just compliment to be nice. If their performance was bad, call them on it. If it was great, tell them why. I've been around too many groups who only want to hear positive feedback and reject any constructive criticism because their egos are too sensitive. Last time I checked, you can learn more from areas you can improve upon, than always being showered with praise.
Low standards. What does "good" really mean? Better than average? When you and I live in the "land of good" everything is the same. The bar is lowered because it slowly disappears. "Good" is a lazy response that we can't learn anything from. It doesn't tell us anything. It's neither hot nor cold. It's in between.
"Good" saps your motivation. It's a generic label. Be bold enough to ask for clarification the next time someone mentions the word "good." Why settle for good, when you can strive to be great?