Only an animal is not pessimistic about life in this material world. A man is capable of knowing the threefold sufferings of material life. There are sufferings of the mind and body, sufferings offered by other living entities, and sufferings forced upon us by natural catastrophes and the laws of nature. The world is full of suffering, but under the spell of maya, illusion, we think we are progressing. Ultimately, whatever we do, death is there to annihilate the results. Under these circumstances, there is no happiness within this material world. We may make all arrangements for happiness, but at any moment, death may capture us. So what happiness can we have here? Therefore an intelligent man is always pessimistic about material life. He knows that he will not be allowed to be happy here. As we further advance, we understand the orders of Krsna: sarva-dharman parityajya mam ekam saranam vraja. "Abandon all religions and just surrender unto Me." [Bg. 18.66] We must surrender to the Supreme Personality of Godhead, and after surrendering and understanding Him fully, we can go to the world that is full of bliss, knowledge, and eternal life. Unless we take a pessimistic view of this material world, we will remain attached to it, and the repetition of birth and death will ensue.
>>> Ref. VedaBase => William James [1842-1910]