"Whatever the present moment contains, accept it as if you had chosen it."
Thought vibration is not as simple as "thinking positive". Positive thinking is probably the most common cliche in self improvement literature. And whilst it is a valid statement there are some pitfalls and challenges associated to positive thinking - or the effort to do so.

So the traditional principle is: think positive and "every little thing is gonna be alright" as Bob Marley used to say. Which means that by being optimistic every situation will always turn out for the best. But thought vibration is more than that, it is a permanent attitude to life.
Thinking positive is definitely an essential attitude to a successful life, however it can lead us in the wrong direction if we rely solely on it. The reasons are:
That's the real challenge. Monks have mastered it, they live much simpler and happier compared to the rest of us, stressed out people. We have a role to play to shape our reality, but equally we already have the all the essential ingredients to be joyful (or "positive") now, regardless of what the future reserves to us.
I close with this very touching story:
The Story of "Misfortune"
A chinese farmer's neighbors came over to offer him their sympathy after his horse ran away. "I'm not so sure it's a misfortune", said the farmer. The neighbors left, shaking their heads.
The next day, the farmer's horse returned, and three wild horses came home with him. The neighbors returned to congratulate the farmer on his good fortune. "I'm not certain that it is good fortune", replied the farmer. The neighbors left, more bemused than before.
Later that week, the farmer's son broke his leg trying to train one of the new horses, and the neighbors came by to offer condolences. "I'm not sure this is a misfortune", said the farmer again. The neighbors left, discussing the man's mental state among themselves.
The next day, the emperor came through, gathering up young men to be in his army. They bypassed the farmer's son, since he had a broken leg.