First, you were born. This in itself is a remarkable achievement. Did you know that each time your father ejaculated (and frankly he did it quite a lot) he produced roughly 25 million spermatozoa - enough to repopulate Britain every two days or so? For you to have been born, not only did you have to be among the few batches of sperm that had even a theoretical chance of prospering - in itself quite a long shot - but you then had to win a race against 24,999,999 or so other wriggling contenders, all rushing to swim the English Channel of your mother's vagina in order to be the first ashore at the fertile egg of Boulogne, as it were. Being born was easily the most remarkable achievement of your whole life. And think: You could just as easily have been a flatworm.
Second, you're alive. For the tiniest moment in the span of eternity you have the miraculous privilege to exist. For endless aeons you did not. Soon you will cease to be once more. That you are able to sit here right now in this one never-to-be-repeated moment, reading this book, eating bonbons, dreaming about hot sex with that scrumptious person from accounts, speculatively sniffing you armpits, doing whatever you are doing - just existing - is really wondrous beyond belief.
Third, you have plenty to eat, you live in a time of peace, and "Tie a Yellow Ribbon Round the Ole Oak Tree" will never be number one again.
If you bear these things in mind, you will never be truly unhappy..."
psst. here's a link to buy the book on amazon.com.