Question: Can we say that every one has his own philosophy by nature?
Answer: As everyone grows up, they develop a set of values: ways they interpret and respond to the world. At the basis of their values lies what Ayn Rand called a "sense of life." A sense of life is formed of subconscious "metaphysical value judgments" that are expressed as an emotional sum. Metaphysical value judgments are judgments about fundamental issues, such as whether the human mind is competent to deal with reality, or whether the individual or the community matters more ethically.
A sense of life is like a philosophy because it is an assessment of the world and our place in it. It's the feeling you have about basic issues. Your sense of life determines how you respond to artwork, and it strongly influences your response to challenges and life choices. Your romantic, political, and cultural inclinations are also affected by your sense of life.
But a sense of life is not a philosophy, because it is fundamentally subconscious. A philosophy, by contrast,?is a system of explicit principles; it is held consciously in conceptual form and can be judged rationally on the basis of the facts. A philosophy can easily be amended as needed. But a sense of life arises out of our experiences, and like many of our basic emotional responses, it is slow to change. A philosophy can be checked for its internal coherence; but a sense of life may simply embrace warring attitudes.
Philosophy has to be discovered or learned. The very idea of philosophy had to be invented by thinkers like the Ancient Greek philosophers or the founders of Chinese philosophy. Sense of life arises naturally from judging and feeling. But philosophy is learned, from the teachings of elders, from priests and mullahs, and by studying serious philosophers.
So, no, not everyone has a philosophy, and philosophy does not come automatically by nature. What comes naturally is a sense of life.