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 the world. It looks at things objectively (yathābhūtam). It does not falsely lull you into living in a fool's paradise, nor does it frighten and agonize 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.
The question has often been asked; Is Buddhism a religion or a philosophy? It does not matter what you call it. Buddhism remains what it is whatever label you may put on it. The label is immaterial. Even the label 'Buddhism' which we give to the teachings of the Buddha is of little importance. The name one gives is inessential.... In the same way Truth needs no label: it is neither Buddhist, Christian, Hindu nor Moslem. It is not the monopoly of anybody. Sectarian labels are a hindrance to the independent understanding of Truth, and they produce harmful prejudices in men's minds.
According to the Buddha's teaching the beginning of the life-stream of living beings is unthinkable. THe believer in the creation of life by God may be astonished at this reply. But if you were to ask him 'What is the beginning of God?' he would answer without hesitation 'God has no beginning', and he is not astonished at his own reply.
There is no unmoving mover behind the movement. It is only movement. It is not correct to say that life is moving, but life is movement itself. Life and movement are not two different things. In other words, there is no thinker behind the thought. Thought itself is the thinker. If you remove the thought, there is no thinker to be found.