Very half-empty here. Actually, more like quarter full I think.
The toll of life with open eyes and critical reasoning has made me very cynical.
Plus, another life-lesson was learning to always anticipate the worst. Then you can work up options and what ifs to help deal with it ahead of time, and approach any situation with your eyes open instead of closed. That has a positive side because it leaves the door open to be pleasant surprised

Which is a way better state of mind for me than a blind "lah lah lah, everything will be fine" - then it isn't - and it comes as a huge shock. One that could be foreseen with some healthy pessimism.
In the work place I find it's the folk with glasses so full they are overflowing whom make all the mistakes.
Another application would be to never get into something that you don't have a way out of! This also requires a mind set of expecting the worst.