It is always a feeling of conflict between being rational and thinking positively, and optimistically.
To an extent, the conflict is there. And one may be better of fooling himself in the right places, than being always 100% rational.
Rationality can bring positive thinking to our life, too.
Most things that do happen to us, have two sides, and in every thing that we would have rather not have, there are positives. Being aware to these actual positives can bring a lot of happiness to our lives.
There is also a practical side to it. We can only get progress in life in the current. Seeing the good sides of every current situation, can help very much in seizing every opportunity we have at this cery moment. We cannot progress by seizing yesterday's opportunities.
Life is highly variable. The advantage player acts every moment to maximize what he can get from what he has now. SOmetimes it is those positives of the current situations that are the best opportunities to pursue.