I found this on the internet, author unknown:

Think of the things that maake you happy

Not of the things that make you sad

Think of the fine and true in mankind

Not the sordid side and bad

Think of the blessings that surround you

Not the ones that are denied

Think of the virtues of your friendships

Not the weak and faulty side

Think of the gains you've made in business

Not the losses you've incurred

Think of the good of you that's spoken

Not some cruel hostile word

Think of the days of health and pleasure

Not the days of hurt and pain

Think of the days alive with sunshine

Not the dismal days of rain

Think of the hopes that lie before you

Not the waste that lies behind

Think of the treasures you have gathered

Not the ones you failed to find

Think of the service you may render

Not the serving self alone

Think of the happiness of others

Aand in this you'll find your own!