Be a balanced optimist. ...

Be a balanced optimist. Nobody is suggesting that you become an oblivious Pollyanna, pretending that nothing bad can or ever will happen. Doing so can lead to poor decisions and invites people to take advantage of you. Instead, be a rational optimist who takes the good with the bad, in hopes of the good ultimately outweighing the bad, and with the understanding that being pessimistic about everything accomplishes nothing. Prepare for the worst but hope for the best - the former makes you sensible, and the latter makes you an optimist.
Be a balanced optimist. Nobody is suggesting that you become an oblivious Pollyanna, pretending that nothing bad can or ever will happen. Doing so can lead to poor decisions and invites people to take advantage of you. Instead, be a rational optimist who takes the good with the bad, in hopes of the good ultimately outweighing the bad, and with the understanding that being pessimistic about everything accomplishes nothing. Prepare for the worst but hope for the best - the former makes you sensible, and the latter makes you an optimist.
 Dale Carnegie

Quotes from the same author

Do you know the most important trait a man can have? It is not executive ability; it is not a great mentality; it is not kindliness, nor courage, nor a sense of humor, though each of these is of tremendous importance. In my opinion, it is the ability to make friends, which, boiled down, means the ability to see the best in man.
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 Dale Carnegie
Happiness doesn't depend on any external conditions, it is governed by our mental attitude.
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 Dale Carnegie
Success is getting what you want. Happiness is wanting what you get.
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 Dale Carnegie
Most of the important things in the world have been accomplished by people who have kept on trying when there seemed to be no hope at all.
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 Dale Carnegie
When fate hands us a lemon, let's try to make lemonade.
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 Dale Carnegie