Kibari, you're a smart one. Sort of building on to that, I think the best way to live is to be subjective to negativity, but open to anything positive.
Well, negativity is a state of mind.
It is entirely up to you how you perceive things (supposing you don't have a chemical imbalance).
It would be more mentally healthy to "be prepared" for bad things (after all, this is what security is for) than to dwell on them.
So yes, indeed prepare, but do not dwell. Constant anxiety nor depression is healthy. The most natural thought state tends to be neutrality whereby positivity is a part of the psychological reward system which helps us to survive. Humans are an animal that in-particularly "over-think" in a cyclical fashion which leads to a downwards spiral of worry and sadness. If you treat your reward system for what it is and keep a neutral outlook on most things while also enjoying the positive things then you will be much more mentally healthy. Though, this is easier said than done but it can be done with meditative things. You can say that negativity is simply the opposite of positivity, our ability to remember what is bad enables us to remind ourselves not to do this again, as a hence experiencing "negativity" creates feelings of discord and it is up to you to realise negativity is something to learn from and not something to dwell upon.
Knowing when to think negatively and positively is really something only your wisdom and instincts can tell you.
Note, that nothing's ever a perfect balance when it comes to mindedness, no one's perfect - not even you. And that's also where evolution comes in.
How close minded or open minded you are depends on your values and positivity/negativity ratio.
Those with positive thinking and emotions tend to be far more successful. The emotion and trigger for epiphany is also most likely experienced by a positive, balanced-minded person because said person is on a "roll" - a "high". Of course the reason why you should not be absolutely positive is because without negativity there is no mental contrast of what is good and worth working towards. In strategic battles, for example, "positive thinking" that leads to cockiness without any skepticism will most likely lead you into being the "over-confident" loser - that is where balanced mindedness is most important. Balanced mindness also promotes survival and creativity in general and since the world is a "creative" community consisting of lifeforms that need to "survive", it's really the best and most natural method of thought.
The only issue is, it is not always easy to be "balanced" and with healthy "positivity".
So many have different values, opinions and beliefs. Close-mindedness often simply takes over as a method of self-preservation, this is a side-effect of the inevitable subjective/relative chaos factor of the universe. Sometimes the most efficient way of mindedness is to continue as you are - but there's always room for revolutionary thinking.
All in all, do not fool the self into thinking too negatively.