Take any bad event that occurs in your life, and if you look hard enough, you will find something good about it. There are ALWAYS exceptions, though.
The key to a healthy perspective is to be able to find these "golden" linings. But don't forget that a bad event is a wonderful opportunity to grow as a human being, so don't forget to learn your lesson, as well.
Say you cheat on a test. This fails you, as the teacher finds out. On the surface you've gotten the crap-end of the stick, but if you look a little deeper, you'll realize that this occurance is trying to teach you honesty.
Now here's where perspective comes in useful, not only in hindsight, as is the case in the above, but also as things are happening.
Perspective determines your reality. It's that simple. If you are standing in 0 degrees celsius in a t-shirt, science dictates that you are going to be cold. While this coldness is unavoidable, it is controllable. It can be limited to a slight briskness in the air instead of a freezing chill. There arer generally a few ways of accomplishing this, but each of these must be believed to a greater degree in order to change your perception:
1) Tell yourself repeatedly that you are not cold. This works really well if you're able to fool your own senses with a mantra, or if you're distractable enough to forget that you are cold. So generally, it doesn't work all that well (for me, anyways).
2) Tell yourself that you are warm. This seems to work more efficiently than telling yourself that you are not cold. Don't ask me why. Positive thinking?
3) Tell yourself that you enjoy being cold. I find that I'm very sense-oriented. If I concentrate on how much I like it, and every particle of cold air moving against my skin, sending shivers throughout my body, then I tend to be cold, but not bothered by it, which is, after all, the real goal of this exercise. You can't change the fact you are cold, as science dictates that one must be cold in these circumstances. You CAN change how much you are affected by it, though.
Or, should none of these work, you could get yourself a sweater.
For any martial artist out there, this works amazingly well with pain, too. It's all about mental control, ie, perception control.