[dudeman13]

Depending on the subject, people's natural state is optimism even if they think they are being realistic. [1] and [2] have a bunch of interesting references on this matter

Appearing smart to dumb people isn't hard, so it doesn't count as a negative about pessimism :)

I won't make a judgement about it being usually right, but being pessimistic can be a tool to counteract the standard optimistic stance if you know people are usually optimistic (aka their expectations overshoot reality) on the subject

[1] https://en.wikipedia.org/wiki/Planning_fallacy

[2] https://en.wikipedia.org/wiki/Optimism_bias