To paint a picture of life is difficult. But asking people about life is sort of like asking about an optical illusion riddle. Optical illusions are pictures and images, which present different views of the same reality. So you find yourself wondering "is it a duck or a rabbit?", "Is a zebra black with white stripes or white with black stripes?" Different people give different answers to the same question. Because sometimes questions are not based on fact or reason, but rather on an individual's point of view.
Being Pessimistically Biased
From a particular vantage point, situations, events, emotions, people and life itself, can all look warped and subjective. Everything can be expressed in terms of colors, black, white and gray. White is seeing everything in a positive light. Such "whiteheads" are also known as optimists. Graybeards are the realists. They view everything based on fact and reason. But the blackheads over here, are the pessimists or the gloomy birds. Pessimists always view things in a negative light.
For any situation the optimists will think positively. The sun will come up tomorrow and life is all about living and experiencing things. If today's not my day, then no problem, there is always a tomorrow.. The logical thinkers will think in a realistic manner If the sun shines today, tomorrow may be cloudy, it depends on the weather forecast, climatic conditions, blah, blah.There is a rhyme and reason for anything's existence. Whereas, pessimists will walk in the negative direction. The glass is half or nearly empty, the sun will not shine tomorrow, it is so obviously going to be cloudy.

An individual may not fall rigidly into any of the 3 groups (optmist, logical, or pessimist) but instead may jump from one group to another, depending on the situation or emotion. Some people are incredibly optimistic about love but can be very realistic when it comes to finances and careers. Then there are effects or biases. Just like prejudice and racism, one can be biased in terms of thinking positively or negatively.
Consider the following situation: An interview is being held for a high-profile job in a Fortune 500 company. It is a dream job and a dream company. The competition is fierce and 2 candidates A and B wait for their respective interviews. A looks around the room and feels hopeful. Yes there are a lot of people, yes the interview might go very rough but inside A is brimming with hope. B in contrast is pessimistic. There are too many people, he'd never get selected, why would such a company choose him, he doesn't have the right qualifications or the necessary experience. He's pretty sure that he will fail miserably. The truth is that both A and B have the same qualifications and experience. Both A and B get through the first round and wait anxiously for the second. A is once again hopeful. B is funnily enough, even more pessimistic. They made a mistake, they think he's someone he's not etc. all sorts of doubts course through his head. Candidate B is thinking negatively or pessimistically in continuation. Even though a positive chance appeared, he still persists in his negativism.
pessimism bias
A biased outlook, that negative things will keep occurring and the rate of their occurrence is very high for a particular individual is called a pessimism bias. A person suffering from this bias, views life as one series of disasters and negative events. The likelihood of something negative occurring is greatly exaggerated in such a biased mind.
If said individual crosses the road, the likelihood of a car hitting him is 95%. The likelihood that he will die is 95%. The likelihood that his accident will not be covered by his life insurance policy, leaving his family destitute, is 105%. Any situation for such an individual is guaranteed to end in failure. The opposite of such a spectrum is an optimism bias, where the individual exaggerates the likelihood of a positive event. In the above scenario, if A thinks he is definitely going to get the job, irrespective of the competition, he is optimistically biased.
A survey conducted by Selima Ben Mansour, Elyès Jouini and Clotilde Napp of the CEREG Université Paris Dauphine, called "Is There a "Pessimistic" Bias in Individual Beliefs?", studied how people view their own luck. Each person was asked a simple question: Imagine that a coin will be flipped 10 times. Each time, if heads, you win. How many times do you think that you will win? Out of a test group of 1,540 individuals, 4 was the answer most gave. The average answer is 5, optimistic being 8 or 9. Yet majority went with 4, which is below average chances of winning. It was also noted that women were more negative as compared to men, with their chances of winning and the elderly are more pessimistic as compared to the young.
In some situations, people can show an obvious and marked pessimism bias and one such situation is the rise and fall of the economy. For non-economists or people who cannot understand the policies of finance and economics, the economy can look very bleak and they tend to exaggerate the rise and fall events in the stock market. They view the current situation of the economy in a very negative view, like it's the end of the financial world and that the success of the past will never come again. But those well-versed in financial jargon and know-how, are realistic that the situation will improve, because nothing lasts forever and this applies to good and bad things.
In summation, any bias in thinking is not good, be it positive or negative. Living life so bleakly and full of negative thinking, ultimately takes a toll on your mental and physical health. Instead of saying "life sucks", keep the Beatles classic tune Ob-la-di, ob-la-da, life goes on, brah!... in mind and think realistically!