na-adjective, noun
A person who tends to see the worst aspect of things or believe that the worst will happen. Often used as a noun or adjectival noun (e.g., ペシミストな人).
彼はいつも悪い方に考えるペシミストだ。
He is a pessimist who always thinks the worst.
ペシミストな見方をすると、計画は失敗するように思える。
From a pessimistic viewpoint, the plan seems likely to fail.