Overthinking isn't bad when you're ruminating about something that's generally positive: how lucky you are to have such a wonderful family, the material you want to have down cold for tomorrow's finance exam, the ideal place to propose to your girlfriend. In other words, thinking deeply pays off when it's something that induces positive emotions in you. You imagine yourself succeeding in whatever it is you're aiming for. You're focused on what you have rather than what you lack. If you're consumed with thoughts that breed negativity -- from how stupid you were for turning down that date to how sure you are that you're going to bomb the presentation this afternoon -- overthinking can have an adverse effect on your physical and mental health. It can lead to anxiety, depression, low self-esteem, and other detrimental conditions. It's a fine line to tiptoe. Indeed, we should all strive to adopt a "half glass full" mentality. I don...