Yes you heard that right positive thinking may not always be the truthful and realistic way of thinking.
Truthful thinking is a balanced way of thinking which is not getting swayed away by too much attraction and positivity and not labelling something as extremely awful.
Too much positivity and over optimism can mislead you and often results in mistakes and failures. Stock market crashes and bubble bursts are a perfect example that shows what happens due to too much optimism.
When you are being overly optimistic or too positive you may not be looking at the true picture and a realistic picture.
a True and realistic picture emerges when you take your time to analyze things from the intellectual point of view. And not be lead by your emotions.
You are thinking in a right direction when you are neither being too positive or too negative. When you are simply understanding everything from an intellectual point of view. You are observing and understanding rather than judging and classifying things into right and wrong.