Overcaution is an excess of wariness about potential dangers. It's important to be alert and thoughtful when you're driving, but overcaution may cause you to drive too slowly and constantly hit the brakes.
Overcaution takes caution, from a Latin root meaning "be on one's guard," and adds over, or "beyond." While caution makes sense, whether you're testing a frozen pond to make sure it's safe for skating or getting a flu shot to avoid getting sick, overcaution goes too far. Overcaution about trusting people makes it harder to make friends, and overcaution at the pool may mean never getting up the nerve to jump off the high diving board.