If positive fails, try Negative.

Sometime you may have observed that your reverse expectation gave you a positive result. And that is true sometimes. Because you can't be the same all the times. You have to change. A student laptop will not be used for reading articles all the time. A student watches movies sometimes. This is change, and it is necessary for our existence. 

So when I have to expect negative? When you think that your positivity is failing. And that is a sign of change. Another answer can be : It depends on your situation. If you have practiced positivity many times, your subconscious mind will tell you.