People says you should have positive attitude. "Hope for the best and prepare for the worst". When I think back in my life, this kind of attitude leads to more disappointment than anything else.
Let's do it the other way. "Expect the worst and prepare for the better". If things go your way, you will be very very happy. If things didn't go your way, you always have plan B, Plan C, Plan D.... to make up for it.