I couldn't agree more. Too much of positive thinking can only bring you heartbreaking disappointment. In as much as it's good to be optimistic and less pessimistic, it's also important to stay with reality. Don't assume things will be better when you know inside of you that it won't so you can start thinking of practical ways to actually make things better. The earlier you become practical and realistic, the better for you. I'm a realist myself even though I am optimistic.
https://www.bath.ac.uk/announcements/time-to-get-real-on-the-power-of-positive-thinking-new-study/ 
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I couldn't agree more. Too much of positive thinking can only bring you heartbreaking disappointment. In as much as it's good to be optimistic and less pessimistic, it's also important to stay with reality. Don't assume things will be better when you know inside of you that it won't so you can start thinking of practical ways to actually make things better. The earlier you become practical and realistic, the better for you. I'm a realist myself even though I am optimistic.