I tihnk for the most part, we have been told that thinking the worst is deflating and to always think positively but, I think that we have it a bit confused. Too much positive and we become complacent.

There are actually studies made about visualization of already having what one wants for the future and those that do it make it less likely that they will go through the motions to get it. It demotivates because the mind is a good simulator and makes the body think it already has achieved the goals.