That's an interesting thought; I feel just the opposite about the pessimism/optimism spectrum. To me, it seems that to allow the negative to affect your mindset overmuch is a far greater negative than a positive

Of course, that is why I try to overcome but it still "feels deeper".

Negativity simply tends to "feel deep". And "feel wise". I am an adult, but you see really a lot of it amongst teenagers, goths etc. basically the more angst and cynicism they have "deeper" and "wiser" they feel.

Or for example look at media like Game of Thrones, it is generally the most negative quotes that "feel deep". "Sharp steel and strong arms rule this world, don't ever believe any different." "You're awful." "It is the world that is awful." This sort of stuff tends to "feel deep" far more than something cheery.

Adults have different reasons for being negative (such as habit), but there is still a certain sense of "feeling deep" lurking which impends developing positivity.

Of course pessimism is far easier! But it still "feels deeper". Most people including me are lazy. If something is easy and has some sort of a reward at all (you feel bad, but at least you feel "deep"), we are likely to do it. Why else you think fast-food driven obesity is such a big deal thes days? :-)

Similarly, a very basic human feature is the sour grapes effect. Optimism is hard, so let's find an excuse to not do it. Well, the excuse is that it is "shallow".

I wonder how it is not so for you... perhaps you are of the minority who is not inherently lazy, who does not automatically go for the smallest resistance, the easiest path and then make excuses. But I am.