There is half a glass of water on the table. Is the glass half empty or half full? This question can represent a situation where there is both opportunity(机会) and trouble, but people with different point of views see the same situation in different ways. Ask yourself this question and see what kind of person you are.
If your answer is "half empty", it shows that you tend to look on the dark side of things. You are a negative-thinking person. You are worried about what you don't have or what you have lost more than what you already or still have. In other words, you are a pessimist(悲观主义者).
If you see the glass as half full, you tend to look on the bright side of things. You are a positive-thinking person. You know you should take the opportunity that comes your way rather than worry about getting into trouble. This is to say, you are an optimist.
We don't live in a perfect world, but if we can change the way we see things, the things we see will change.