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.