This is not about being blind and rushing into things. This is about being in a state where you can make decisions. Compare that to a state in which you can only sit and wait. In other words, you can be positive while remaining a realist and overall cold-blooded when you make your trading decisions. I see no conflict or contradiction here. In fact, being realistic already assumes having a positive attitude.
"This is about being in a state where you can make decisions." That's what I've meant with rushing into things, making rational decisions depending on the way of your thinking (pessimistic, optimistic). No, this is some deeper philosophy that I will not be getting into, but being realistic doesn't have to do anything with being pessimistic or optimistic.
In a bad situation, you can be a pessimist and think that it could not get worse, an optimist that it will get better and a realist where you see the situation how it actually is.