Pesimits predict bad things in foward and are prepared for them much better..but their present has limited happyness as exchange
Optimists see the present but live in bright future...they live in future and think of best possible outcomes but they can misscalculate and a lot things can turn wrong then.
Realists see world as it is. They are people who live in present, when they see bad thing they are sad, think most possible/realistic solutions out and when life is good they live it good. They don't trick their mind that its "not that bad as it could be", neither they say "omgosh I'm so down, my life sux". They just deal with it
Everything is good as long you don't go into extremes...Also some people keep changing between optimist and pesimist too much...then they get worst of all -> the unstable mind.
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For me being realist is best I think. But that don't mean its necessary good for all people!</em>