Buddhism is a non-theistic religion. Unlike many other religions it does not believe in a god or a creator. It is not only a religion but also a philosophy with a moral discipline. It originated in north eastern India and was founded by Gautama Buddha. Today, Buddhism has become one of the major religions in the world with more than 500 million adherents. Prince Siddhartha Gautama who later became Gautama Buddha having realised the immense human suffering had looked for a way of easing their pain and suffering. He pursued strict spiritual disciplines to become an enlightened being. Having achieved enlightenment, he preached a path of salvation to his followers so that they could escape the samsaric cycle of suffering, rebirth and death. In brief the entire teaching of the Lord Buddha can be summed up in one stanza from the Dhammapada. “Sabba papassa akaranam kusalassa upasampada sacitta pariyodapanam etan buddhana sasanam” (not to do evil, to cultivate merit, to purify ones mind, this is the teaching of the Buddha}.  

 Criticism of Buddhism has taken many forms. Some incline to the view that Buddhism is overly pessimistic in outlook and always takes a gloomy and melancholic view of life. While others were of the opinion that Buddhism was unscientific, idealistic and impractical. These misconceptions have prevailed from the time of Buddha to this day. It should be stated that these beliefs are fallacious and misleading as Buddhism is neither pessimistic nor optimistic. If anything at all it is realistic as it takes a realistic and dispassionate view of life and of the world and teaches us to look at things as they really are. Buddhism promotes rational and empirical investigation and invites people to put the teachings of the Buddha to test before accepting it. Buddha does not stop at analysing suffering [dukkha] but proceeded to show us the practical way out of it, which is the Noble Eightfold Path.

 The erroneous view that Buddhism is pessimistic has come about as a result of many scholars giving a restricted meaning to the word dukkha (Suffering) in the First Noble Truth. They have interpreted dukka (suffering) as nothing but suffering and pain. This has led many to regard Buddhism as a pessimistic religion. But viewed from a Buddhist perspective the word dukkha (suffering) has a deeper and wider connotation and dimension. 
It should be noted that other than the ordinary meaning of  dukkha (suffering), the word dukkha in the First Noble Truth   also connotes  such things as ‘’imperfection” “impermanence” and “insubstantiality”. 

 Walpola Rahula Thero in his book “What the Buddha Taught” has stated thus: “first of all, Buddhism is neither pessimistic nor optimistic. If anything at all, it is realistic, for it takes a realistic view of life and world. It looks at things objectively (yathabhutam). It does not falsely lull you into living in a fool’s paradise nor does it frighten and agonise you with all kinds of imaginary fears and sins. It tells you exactly and objectively what you are and what the world around you is, and shows you the way to perfect freedom, peace, tranquility and happiness”.  

  Pessimism is a philosophy of suffering while Buddhism is philosophy of the relief of suffering. Had Lord Buddha in his discourse proclaimed that there was nothing but misery in life and there was no happiness to be found anywhere without showing us a way out of it, we will be justified in characterising Buddhism as pessimistic. 
It is true that the Buddha exposed the unhappy part of life. However, while doing so he explained the way to come out of it.

"Buddhism is neither pessimistic nor optimistic.If anything at all it is realistic as it takes a realistic and dispassionate view of life and of the world and teaches us to look at things as they really are"

Buddhism does not countenance melancholic, sorrowful, gloomy attitude to life and it does not foster an attitude of hopelessness to life. Lord Buddha didn’t ask his adherents to contemplate only the gloomy side of life. He did not expect them to brood over misery only, but wanted them to know both happy and sad side of life are equally fleeting and impermanent. 

No one can deny the reality of suffering associated with birth, decay old age death, association with the unpleasant and disassociation from the pleasant. In reality there is none in the  whole world other than Lord Buddha who can be described as preacher of happiness or sukhavadi. A true Buddhist is the happiest of all beings.   
  Buddhism is a religion of salvation. It is an ethical philosophy which preached the unsatisfactory nature of the world.  Unlike other religions in the world which talk about almighty god on whom people depend for salvation. According to Buddhism, one is indeed ones own lord {attahiattanonatho}.

"Buddha does not stop at analysing suffering [dukkha] but proceeded to show us the practical way out of it, which is the Noble Eightfold Path"

  The entire teaching of the Buddha when summed up amounts simply to insights into “impermanence” [annicca] suffering or unsatisfactoriness” [dukkha] and “non-selfhood” [annitta]. These three characteristics were the aspects of teaching which the Buddha stressed more than any other. The three characteristics annicca, dukkha and anantta which facts of life can be realised and grasped by everyone. Even the most placid person would admit that dukkha is omnipresent and universal. This truth can be easily realised by anyone who can think soberly and dispassionately. It can be seen everywhere around us. Infatuation with transient pleasures prevent us from seeing things as they truly are. 

 Walpola Rahula Thero in his book states the Buddha does not deny happiness in life when he says there is suffering. On the contrary he admits different forms of happiness, both material and spiritual, for laymen as well as for monks. In the Anguttara-Nikaya, one of the five original collections in Pali containing the Buddha’s discourses, there is a list of happinesses (sukhani), such as the happiness of family life and the happiness of the life of a recluse, the happiness of sense, pleasures and the happiness of renunciation, the happiness of attachment and the happiness of detachment, physical happiness and mental happiness etc.
Misery arises because of craving and aversion, which in turn arise from tanha. If these causes are eradicated, the root cause of misery is eradicated. Lord Buddha said pain is followed by pleasure and pleasure is followed by pain In other words, pleasure and pain follow each other as day follows night.

If you observe the reality around us, it is evident it consists of birth, sickness, old age, sorrow, pain, distress, decay, grief, death lamentation etc. Empirical observation of human existence makes it clear. Buddha laid emphasis on knowing things as really are [yathabhutanana] if you take a critical look at life and all its concomitants it is clear to everyone everything is in a state of flux. Life is a succession of fleeting moments of arising and dissolution. And every cell in the body of a being would die and be replaced by a new cell which in turn would die to be replaced by another. From conception to death the process goes on uninterrupted. Buddhas definition of suffering is clear and empirical to anyone.   

"Lord Buddha said pain is followed by pleasure and pleasure is followed by pain. In other words, pleasure and pain follow each other as day follows night"

When Buddha had passed away sukka, the king of Dewas, the sutta Maha parinama sukka uttered the following - Impermanent are all component things, they arise and cease, that is their nature. They come into being and pass away. Release from them is bliss. (Annicca vata sankara Uppada vaya dhammino Uuppajjitva nirujjhanti Tesam vupa samo sukho).   
   When Buddha preached “he who sees dukkha sees also the arising of dukkha, sees also cessation of dukkha, and sees also the path leading to the cessation of dukkha”. This does not make the life of a Buddhist melancholy or sorrowful at all, as some people wrongly imagine.